Catalysts and their preparation methods

Abstract

This disclosure relates to a catalyst and a method for preparing the same. Specifically, this disclosure relates to an electrode catalyst configured to support non-noble metal particles, noble metal particles, or noble metal particles doped with nitrides on a nitrogen-doped carbon support having a two-dimensional planar crystal structure or a three-dimensional polyhedral crystal structure, thereby exhibiting higher catalytic activity.

Description

Technical Field

[0001] This disclosure relates to a catalyst and a method for preparing the same. Background Technology

[0002] The statements in this section are provided only as background information in connection with this disclosure and may not constitute prior art.

[0003] To improve electrode reaction rates, polymer electrolyte membrane fuel cells must use the precious metal platinum as a catalyst. Platinum is expensive and its reserves are limited.

[0004] Catalysts for replacing platinum with non-platinum transition metals linked to nitrogen via coordination bonds are under investigation, particularly porous metal-organic frameworks (MOFs), which are composites of transition metals, nitrogen, and carbon. These complexes exhibit excellent performance due to their large specific surface area, micropores, and coordination bonds between the transition metal and nitrogen, and their use as electrode catalysts in non-platinum fuel cells has been reported in numerous studies. However, the development of non-platinum catalysts with sufficiently high performance is rarely reported.

[0005] When using small amounts of platinum, carbon, with its large specific surface area and excellent pore structure, is used as a platinum support to increase its reactivity relative to mass by loading small-sized particles. Additionally, it has been reported that nitrogen, sulfur, phosphorus, etc., are added to existing carbon structures, thereby improving performance through changes in electronic structure.

[0006] To reduce platinum usage and improve the low activity of non-platinum catalysts, we found that composite catalysts combining the two systems are ideal, considering both activity and price. However, the use of iron generates hydroxyl groups in side reactions, thus shortening the fuel cell's lifespan. Summary of the Invention

[0007] This disclosure provides a method for preparing electrode catalysts for fuel cells or water electrolysis cells that can effectively utilize both precious and non-precious metals.

[0008] This disclosure provides an electrode catalyst that reduces the content of precious metals by using non-precious metals other than iron (Fe) and has high activity.

[0009] This disclosure provides a catalyst comprising: a carbon support doped with nitrogen; and solid particles supported on the surface of the carbon support, wherein the solid particles comprise any one of the particles selected from the group consisting of non-precious metal particles, precious metal particles, nitrogen-containing precious metal particles, and combinations thereof.

[0010] Carbon supports can have a two-dimensional planar crystal structure or a three-dimensional polyhedral crystal structure.

[0011] The porosity of the carbon support can range from 10% to 85%.

[0012] Nitrides can include cobalt nitrides.

[0013] Solid particles may include any type of particle selected from the group consisting of precious metal particles, precious metal particles containing cobalt nitrides, and combinations thereof.

[0014] Non-precious metal particles may include cobalt, and precious metal particles may include platinum.

[0015] The catalyst can be contained in the electrodes of a fuel cell or a water electrolysis cell.

[0016] In addition, this disclosure provides a method for preparing a catalyst, comprising: preparing a support by synthesizing a metal precursor and an alkylimidazolium; preparing a nitrogen-doped carbon support by subjecting the support to a primary heat treatment; subjecting the carbon support to a secondary heat treatment; purifying the carbon support by removing metal particles through acid treatment; and preparing a composite catalyst by subjecting the carbon support to a tertiary heat treatment.

[0017] The carrier may include ZIF-67 as a zeolite imidazole ester backbone.

[0018] The initial heat treatment can be carried out in an inert gas atmosphere at a temperature of 25°C to 1000°C for 10 to 300 minutes, and the secondary heat treatment can be carried out at a proton concentration (pH) below 7 at a temperature of 60°C to 100°C for 2 to 10 hours.

[0019] Carbon supports prepared by initial heat treatment can include cobalt particles on their surface.

[0020] The carbon support can be added to the solvent along with platinum and then subjected to a secondary heat treatment.

[0021] The carbon support after secondary heat treatment may include particles selected from the group consisting of cobalt, nickel, platinum and combinations thereof on its surface.

[0022] Acid treatment can be carried out in hydrochloric acid aqueous solution at a temperature of 90°C to 120°C for 1 to 3 hours.

[0023] Metal particles removed from a carbon support by acid treatment may include pure cobalt that is not bonded to platinum.

[0024] The three heat treatments can be carried out in ammonia at a temperature of 300°C to 600°C for 10 to 60 minutes.

[0025] In addition, this disclosure provides a method for preparing a catalyst, comprising: preparing a support by synthesizing a metal precursor and an alkylimidazolium; preparing a nitrogen-doped carbon support by subjecting the support to a primary heat treatment; removing metal particles from the surface of the carbon support by acid treatment; and preparing a composite catalyst by subjecting the carbon support to a secondary heat treatment.

[0026] The carbon support prepared by the initial heat treatment can include cobalt particles on its surface, and the cobalt particles can be completely removed from the surface of the carbon support by acid treatment.

[0027] The carbon support can be added to the solvent along with platinum and then subjected to a secondary heat treatment.

[0028] The carbon support after secondary heat treatment can include platinum particles on its surface.

[0029] According to this disclosure, a method for preparing an electrode catalyst for fuel cells or water electrolysis cells that can effectively utilize both precious and non-precious metals can be provided.

[0030] According to this disclosure, an electrode catalyst with high activity can be provided by using non-precious metals other than iron (Fe) to reduce the content of precious metals.

[0031] The effects of this disclosure are not limited to those described above, and should be understood to include all effects that can be reasonably expected from the following description.

[0032] Other applicable areas will become apparent from the description provided in this section. It should be understood that the descriptions and specific examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0033] To make this disclosure readily understandable, various forms of the disclosure will now be described by way of example and with reference to the accompanying drawings, in which:

[0034] Figure 1 One form of catalyst of this disclosure is shown, comprising nitrogen-containing noble metal particles and a nitrogen-doped carbon support;

[0035] Figure 2 One form of catalyst of this disclosure is shown, comprising noble metal particles and a nitrogen-doped carbon support;

[0036] Figure 3 An example of a catalyst according to the present disclosure is shown, comprising nitrogen-containing noble metal particles and a nitrogen-doped carbon support having a two-dimensional planar crystal structure;

[0037] Figure 4An example of a catalyst according to the present disclosure is shown, comprising noble metal particles and a nitrogen-doped carbon support having a two-dimensional planar crystal structure;

[0038] Figure 5 This is a flowchart illustrating a process for preparing an electrode catalyst comprising nitrogen-doped noble metal particles according to one form of the present disclosure;

[0039] Figure 6 The process of preparing a catalyst by converting a support into a two-dimensional planar crystal structure is shown.

[0040] Figure 7 The process of preparing catalysts using a support with a three-dimensional crystal structure is shown;

[0041] Figure 8 This is a flowchart illustrating the process of preparing an electrode catalyst containing noble metal particles;

[0042] Figure 9 The process of preparing a catalyst by converting a support into a two-dimensional planar crystal structure is shown.

[0043] Figure 10 The process of preparing catalysts using a support with a three-dimensional crystal structure is shown;

[0044] Figures 11A to 11C The results of observing the electrode catalyst prepared in Example 1 using scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy are shown.

[0045] Figures 12A to 12F The results of energy-dispersive X-ray spectroscopy for the electrode catalyst of Example 1 are shown;

[0046] Figures 13A to 13F The results of observing the electrode catalyst prepared in Example 2 using transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy are shown.

[0047] Figures 14A to 14G The results were obtained by observing the electrode catalyst prepared in Example 3 using transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy.

[0048] Figure 15 This is a graph showing the results of Experiment Example 1;

[0049] Figure 16A and Figure 16B This is a graph showing the results of Experiment Example 2;

[0050] Figures 17A to 17F This is a graph showing the results of Experiment Example 3;

[0051] Figure 18A and Figure 18B This is a graph showing the results of Experiment Example 4; and

[0052] Figures 19A to 19D This is a graph showing the results of Experiment Example 5.

[0053] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of this disclosure in any way. Detailed Implementation

[0054] The following description is exemplary in nature only and is not intended to limit this disclosure, its application, or its uses. It should be understood that in all the drawings, corresponding reference numerals denote the same or corresponding parts and features.

[0055] For clarity of this disclosure, the dimensions of the structures are shown as larger than their actual dimensions. It will be understood that although terms such as “first” and “second” may be used herein to describe various elements, these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, an “first” element discussed below may be referred to as a “second” element without departing from the scope of this disclosure. Similarly, a “second” element may also be referred to as a “first” element. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise.

[0056] It will be further understood that the terms "comprising," "including," "having," etc., as used in this specification specify the presence of the stated features, quantities, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, 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 may be directly on the other element, or there may be intermediate elements between them. Similarly, when an element such as a layer, film, region, or sheet is referred to as being "under" another element, it may be directly under the other element, or there may be intermediate elements between them.

[0057] Unless otherwise stated, all figures, values, and / or representations indicating the quantities of components, reaction conditions, polymer compositions, and mixtures used herein should be considered approximations that include various uncertainties and other factors inherent in obtaining these values ​​that can affect the measurement results, and are therefore to be understood as being modified by the term "about" in all cases. Furthermore, when numerical ranges are disclosed in this specification, the ranges are continuous and include all values ​​from the minimum to the maximum of the range, unless otherwise stated. Additionally, when such ranges pertain to integer values, they include all integers from the minimum to the maximum value, unless otherwise indicated.

[0058] In this specification, when describing the range of a variable, it should be understood that the variable includes all values, including the endpoints described within the range. For example, the range "5 to 10" should be understood to include any subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and the individual values ​​of 5, 6, 7, 8, 9, and 10, and will also be understood to include any value between valid integers within the range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. Similarly, the range "10% to 30%" will be understood to include subranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and all integers including values ​​up to 30% such as 10%, 11%, 12%, 13%, etc., and will also be understood to include any value between valid integers within the range, such as 10.5%, 15.5%, 25.5%, etc.

[0059] This disclosure relates to a catalyst and a method for preparing the same. Specifically, this disclosure relates to an electrode catalyst configured to support non-noble metal particles, noble metal particles, or nitride-containing noble metal particles on a carbon support having a two-dimensional planar crystal structure or a three-dimensional polyhedral crystal structure and being doped with nitrides, thereby exhibiting higher catalytic activity.

[0060] Figures 1 to 4 The structure of the catalyst of this disclosure is shown. The catalyst of this disclosure is described with reference to these figures, and also with reference to… Figures 5 to 10 The preparation method of the catalyst disclosed herein is described step by step.

[0061] Catalyst

[0062] The catalyst disclosed herein includes a support and solid particles supported on the surface of the support. Here, the solid particles may include any particle selected from the group consisting of non-precious metal particles, precious metal particles, nitride-containing precious metal particles, and combinations thereof.

[0063] In one form, the support disclosed herein is a nitrogen-doped carbon support.

[0064] Depending on the requirements, the carrier disclosed herein may have a two-dimensional planar crystal structure or a three-dimensional polyhedral crystal structure.

[0065] Figure 1 and Figure 2 Catalysts comprising a carbon support having a three-dimensional polyhedral crystal structure and being doped with nitrogen are shown. Figure 3 and Figure 4 Catalysts comprising a carbon support having a two-dimensional planar crystal structure and being doped with nitrogen are shown.

[0066] The catalyst disclosed herein includes a support and particles attached to the surface of the support, the particles being selected from any of the group consisting of non-precious metals, precious metals, nitride-containing precious metals, and combinations thereof. The particles on the support may be selected as needed and may contain nitride-containing precious metals with beneficial effects. Here, the nitride may include cobalt nitride, the non-precious metal may include cobalt, and the precious metal may include platinum.

[0067] Figure 1 A catalyst (CoN-Pt / CoNC-block) according to the present disclosure is shown, comprising nitride-containing noble metal particles 301 and nitrogen-doped carbon support 101. Figure 2 Another form of catalyst (Pt / CoNC-block) according to this disclosure is shown, which comprises noble metal particles 300 and nitrogen-doped carbon support 101.

[0068] Figure 1 and Figure 2 The carbon support has a three-dimensional polyhedral crystal structure. In one form, the diameter of the carbon support is approximately 20 to 1000 nm. Moreover, the porosity of the carbon support is approximately 30% to 85%.

[0069] Figure 3 Another form of catalyst (CoN-Pt / CoNC-2D) according to this disclosure is shown, which includes nitride-containing noble metal particles 301 and nitrogen-doped carbon support 111 having a two-dimensional planar crystal structure. Figure 4 Another form of catalyst (Pt / CoNC-2D) according to this disclosure is shown, which includes noble metal particles 300 and nitrogen-doped carbon support 111 having a two-dimensional planar crystal structure.

[0070] Figure 3 and Figure 4 The carbon support has a two-dimensional planar crystal structure. Here, the thickness of the carbon support is 10 nm to 200 nm, and the diameter is 30 nm to 5000 nm. Furthermore, the porosity of the carbon support is 10% to 60%.

[0071] The methods for preparing electrode catalysts disclosed herein can be broadly classified into two types based on the type of particles included on the support. Specifically, the methods for preparing electrode catalysts can be categorized into methods for preparing electrode catalysts including nitrogen-containing noble metal particles and methods for preparing electrode catalysts including noble metal particles.

[0072] Process for the preparation of a catalyst comprising noble metal particles containing a nitrogen compound

[0073] The method for preparing a catalyst comprising nitrogen-containing noble metal particles according to the present disclosure may include: preparing a support by synthesizing a metal precursor and an alkylimidazolium; preparing a carbon support with exposed non-noble metal and doped with nitrogen by subjecting the support to a primary heat treatment; subjecting the carbon support to a secondary heat treatment; purifying the carbon support by acid treatment of the carbon support with exposed non-noble metal to remove metal particles from its surface; and preparing a composite catalyst by subjecting the carbon support with removed metal particles to a tertiary heat treatment.

[0074] Figure 5 This is a flowchart illustrating the preparation process of the electrode catalyst of this disclosure. Figure 6 and Figure 7 The preparation processes for various types of catalysts are illustrated. (Refer to...) Figures 5 to 7 The following describes the steps involved in the preparation of the catalyst.

[0075] Preparation of the support (S1)

[0076] Support 100 was prepared by synthesizing a metal precursor and an alkyl imidazole.

[0077] In one form of this disclosure, the metal precursor may include cobalt nitrate hydrate (Co(NO3)2·6H2O), and the alkyl imidazole includes 2-methylimidazolium.

[0078] The carrier 100 includes a zeolitic imidazolate framework (ZIF) with a three-dimensional polyhedral crystal structure, and preferably includes ZIF-67 (Co(C4N2H5)2).

[0079] The support 100 includes carbon, nitrogen, hydrogen and cobalt, and in another form, the support 100 is configured such that carbon, nitrogen and hydrogen form the basic framework of the support 100, and cobalt is linked to a portion of the nitrogen contained in the basic framework by coordination bonds.

[0080] In this disclosure, a two-dimensional planar crystal structure can be imparted to the carrier 100 as needed by transforming the crystal structure.

[0081] The support 110 having a two-dimensional planar crystal structure is prepared by adding a support 100 having a three-dimensional polyhedral crystal structure and cobalt nitrate hydrate together to a solvent and carrying out a hydrothermal reaction. Here, the solvent includes methanol. The weight ratio of the support 100 and cobalt nitrate hydrate added to the solvent is from 1:1 to 1:3.

[0082] The hydrothermal reaction can be carried out at a temperature of 140°C to 180°C for 30 minutes to 5 hours, and preferably at a temperature of 150°C to 160°C for 1 hour to 2 hours.

[0083] Figure 6 The process of preparing a catalyst using a support 110 that has been converted into a two-dimensional planar crystal structure is shown. Figure 7 The process of preparing a catalyst using a support 100 with a three-dimensional polyhedral crystal structure without hydrothermal reaction is shown.

[0084] In this disclosure, the shape of the support 100 determines the shape of the final catalyst, and for the purposes of this disclosure, a support 110 having a two-dimensional planar crystal structure is preferably used.

[0085] For ease of description, the description in this disclosure is as follows: Figure 6 The process for preparing the catalyst is shown.

[0086] Initial heat treatment (S2)

[0087] The support 110 is subjected to a primary heat treatment to prepare a nitrogen-doped carbon support 111 with exposed non-precious metals. Specifically, the support 110 is heat-treated in an inert gas atmosphere to include non-precious metal particles 200 on the support 110 and to convert the support 110 into a nitrogen-doped carbon support 111.

[0088] In this disclosure, the non-precious metal particles 200 included on the support 110 include cobalt. Here, the cobalt included on the support 110 is derived from cobalt ions in a conventional support that are coordinated to nitrogen. Specifically, during the carbonization process by initial heat treatment, the cobalt ions linked by coordination bonds are reduced and precipitated on the surface of the carbon support 111.

[0089] In this disclosure, the doped nitrogen originates from nitrogen bonded to carbon in a conventional carrier to form the basic framework. Specifically, the carbon lattice is doped with nitrogen during carbonization via an initial heat treatment. Here, cobalt precipitates on the surface of the nitrogen-doped carbon.

[0090] In one embodiment, the initial heat treatment may be carried out at a temperature of 25°C to 1000°C for 10 to 300 minutes, and the inert gas may include nitrogen (N2).

[0091] In another form, the initial heat treatment is carried out at 800°C for 30 to 120 minutes under the following conditions: the temperature is increased from 25°C to 800°C at a rate of 5°C / minute in a nitrogen atmosphere.

[0092] Secondary heat treatment (S3)

[0093] The nitrogen-doped carbon support 111 and the non-precious metal particles 200 on the carbon support 111 are heat-treated. Specifically, the carbon support 111, which includes non-precious metal particles 200 on its surface and is doped with nitrogen, is added to a solvent along with a precious metal to prepare a mixture, and the mixture is then heat-treated.

[0094] In this disclosure, the added noble metal is loaded onto the surface of the non-noble metal particles 200 via a galvanic conversion reaction, and the non-noble metal particles 200 are loaded onto a nitrogen-doped carbon support 111.

[0095] The noble metal added to the solvent is added in the form of an ionic solution, and the solution preferably contains platinum ions. Here, platinum is provided in the form of chloroplatinic acid (H₂PtCl₆). Specifically, platinum ions are reduced on the non-noble metal particles 200 and precipitate in particulate form, and some of the non-noble metal particles 200 are oxidized and dissolved in the solvent in ionic form.

[0096] Solvents may include ethylene glycol (EG).

[0097] The proton concentration (pH) of the mixture is approximately 7 or less.

[0098] The heat treatment is carried out at a temperature of 60°C to 100°C for 2 to 10 hours.

[0099] Through the heat treatment disclosed herein, the nitrogen-doped carbon support 111 comprises particles selected from the group consisting of non-precious metals, precious metals, and combinations thereof on its surface. Here, the non-precious metal particles may include cobalt, and the precious metal particles may include platinum.

[0100] Purification (S4)

[0101] The carbon support 111, which has exposed non-precious metals and is doped with nitrogen, is purified by acid treatment to remove metal particles from its surface. Specifically, in the purification step, pure non-precious metal particles 200 adhering to the nitrogen-doped carbon support 111 are removed by acid treatment, and only non-precious metal particles 201 contained in the precious metal particles 300 are retained. Here, the pure non-precious metal particles 200 are those that, in this disclosure, neither adhere to nor contact any precious metal particles.

[0102] Acid treatment is performed by dispersing the washed carbon support 111 in a solvent containing acid and then carrying out a hydrothermal reaction. Specifically, in the purification step, the nitrogen-doped carbon support 111 obtained through a secondary heat treatment is washed with distilled water and ethanol, dried, and dispersed in a solvent, followed by a hydrothermal reaction. Here, the solvent used may include hydrochloric acid, and the hydrothermal reaction can be carried out at a temperature of 90°C to 120°C for 1 to 3 hours.

[0103] Non-precious metal particles 200 are removed from the surface of carbon support 111 by a hydrothermal reaction in a solvent containing hydrochloric acid, and some non-precious metal particles 201 present on the precious metal particles 300 are also removed.

[0104] Three heat treatments (S5)

[0105] The composite catalyst was prepared by subjecting a carbon support 111, which includes noble metal particles 300 containing non-noble metal particles 201 on its surface and is doped with nitrogen, to three heat treatments. Specifically, the carbon support 111, which includes platinum particles (some of which include cobalt particles) on its surface and is doped with nitrogen, was subjected to three heat treatments in an ammonia (NH3) gas atmosphere to prepare the composite catalyst.

[0106] During heat treatment, ammonia, together with non-precious metal particles 201 formed on the surface of the precious metal particles 300, synthesizes into nitrides. Nitrides are formed on the surface of the precious metal particles 300 through three heat treatments in an ammonia atmosphere.

[0107] Nitrides include cobalt nitrides.

[0108] The three heat treatments can be carried out in an ammonia atmosphere at a temperature of 300°C to 600°C for 10 to 60 minutes.

[0109] A composite catalyst comprising nitride-containing noble metal particles 301 and a carbon support 111 with nitride-containing noble metal particles 301 on its surface and doped with nitrogen can be prepared by heat treatment.

[0110] Process for the preparation of a catalyst comprising noble metal particles

[0111] The method for preparing an electrode catalyst including noble metal particles according to this disclosure may include: preparing a support by synthesizing a metal precursor and an alkylimidazolium; preparing a carbon support with exposed non-noble metal and doped with nitrogen by subjecting the support to a primary heat treatment; purifying the carbon support by removing metal particles from its surface through acid treatment; and preparing a composite catalyst by subjecting the carbon support to a secondary heat treatment.

[0112] Figure 8 This is a flowchart illustrating the preparation process of the electrode catalyst according to the present disclosure. Figure 9 andFigure 10 The preparation processes for various types of catalysts are illustrated. (Refer to...) Figures 8 to 10 The following describes the steps involved in the preparation of the catalyst.

[0113] Preparation of the support (S'1)

[0114] Support 100 is prepared by synthesizing a metal precursor and alkylimidazolium. This step is the same as the step in preparing the support (S1) in the above-described method for preparing electrode catalysts including doped noble metal particles with nitrides, therefore its description is omitted. For ease of description, the description is as follows: Figure 9 The process for preparing the catalyst is shown.

[0115] Initial heat treatment (S′2)

[0116] A carbon support 111 comprising non-noble metal particles 200 and doped with nitrogen is prepared by performing a primary heat treatment on the support 100. This step is the same as the primary heat treatment step (S2) in the above-described method for preparing an electrode catalyst comprising noble metal particles doped with nitrides, and therefore its description is omitted.

[0117] Purification (S'3)

[0118] Metal particles are removed from the surface of a nitrogen-doped carbon support 111 by acid treatment. Specifically, non-precious metal particles 200 formed on the carbon support 111 during the initial heat treatment are removed by acid treatment, thereby obtaining a nitrogen-doped carbon support 111.

[0119] In this disclosure, the non-precious metal particles 200 that are removed are cobalt particles.

[0120] In this step, acid treatment is performed as follows: a carbon support 111, whose surface includes non-precious metal particles 200 and is doped with nitrogen, is dispersed in a solvent and subjected to a hydrothermal reaction. Here, the solvent includes hydrochloric acid, and the hydrothermal reaction is carried out at a temperature of 90°C to 120°C for 1 to 3 hours.

[0121] A carbon support 111 that does not contain any metal particles and is doped with nitrogen can be formed through a hydrothermal reaction.

[0122] Secondary heat treatment (S'4)

[0123] A composite catalyst comprising a carbon support 111 containing noble metal particles 300 and doped with nitrogen on its surface is prepared by a secondary heat treatment of a carbon support 111 that does not contain any metal particles on its surface. Specifically, the carbon support 111 is added together with the noble metal to a solvent to form a mixture, and the mixture is then heat-treated. Here, the solvent may include ethylene glycol (EG).

[0124] The proton concentration (pH) of the mixture is 7 or less.

[0125] The heat treatment is carried out at a temperature of 60°C to 150°C for 2 to 10 hours.

[0126] Through the heat treatment disclosed herein, the nitrogen-doped carbon support 111 can include only noble metal particles 300 on its surface. Here, the noble metal particles 300 include platinum.

[0127] Electrode

[0128] This disclosure provides an electrode comprising a catalyst prepared by the above-described catalyst preparation method. More specifically, the catalyst of this disclosure may be included in the electrode of a fuel cell or a water electrolysis cell.

[0129] The catalyst may include an electrode catalyst containing a carbon support with nitrogen-containing noble metal particles on its surface and doped with nitrogen, or an electrode catalyst containing a carbon support with noble metal particles on its surface and doped with nitrogen.

[0130] The following examples will help to better understand this disclosure. However, these examples are provided for illustrative purposes only and should not be construed as limiting the scope of this disclosure.

[0131] Preparation Example 1 (CoN-Pt / CoNC-2D)

[0132] An aqueous solution obtained by dissolving the metal precursor Co(NO3)2·6H2O (3.1 mmol) in 6 ml of distilled water was supplied at a rate of 5 ml / h and mixed with an aqueous solution obtained by dissolving 2-methylimidazole (12.2 mmol) in 40 ml of distilled water. The mixture was stirred for 6 hours and then centrifuged and dried to synthesize a support (ZIF-67) with a polyhedral crystal structure.

[0133] ZIF-67 (0.5 g) and cobalt nitrate hydrate Co(NO3)2·6H2O (1.0 g) were uniformly mixed in methanol, and then subjected to a hydrothermal reaction at 160 °C for 2 hours to convert the support into a two-dimensional planar crystal structure.

[0134] In an inert gas (N2) atmosphere, the temperature of a carrier (2.0 g) with a transformed crystal structure was increased from 25 °C to 800 °C at a rate of 5 °C / min, and then heat-treated at 800 °C for 1 hour to form a carbon carrier (Co / CoNC-2D) with cobalt non-noble metal particles on the surface and doped with nitrogen.

[0135] A carbon support (Co / CoNC-2D) (0.1 g) was mixed with a platinum solution (40 μl, 1.93 M) in ethylene glycol solvent (EG, 40 ml). The pH was then adjusted to approximately 7 using an aqueous KOH solution. The mixture was stirred and heat-treated at 80 °C for 8 hours. After washing with distilled water and ethanol, the mixture was dried and dispersed in a 0.5 M aqueous hydrochloric acid solution. The mixture was then subjected to a hydrothermal reaction at 100 °C for 2 hours to remove pure cobalt non-precious metal particles from the surface of the carbon support. Finally, the mixture was dried to prepare a carbon support with platinum particles attached to its surface.

[0136] Subsequently, the electrode catalyst (CoN-Pt / CoNC-2D) was prepared by heat treatment at 500°C for 30 minutes in an ammonia atmosphere, comprising a nitrogen-doped carbon support and platinum particles containing cobalt nitrides attached to the surface of the carbon support.

[0137] Figure 11A The scanning electron microscope (SEM) images of the electrode catalyst prepared above are shown. Figure 11B The image shown is a transmission electron microscope (TEM) image of the electrode catalyst. Figure 11C High-resolution TEM images of the electrode catalyst and the platinum particle size distribution are shown.

[0138] Reference Figures 11A to 11C As can be seen, the carbon support included in the electrode catalyst has a two-dimensional planar crystal structure in which pores are formed and platinum particles with a size of 2 to 4 nm are uniformly distributed.

[0139] Figures 12A to 12F The results of qualitative and quantitative analysis of the surface of the electrode catalyst prepared above using energy-dispersive X-ray spectroscopy (EDS) are shown.

[0140] Reference Figures 12A to 12F It can be seen that platinum, cobalt, and nitrogen are uniformly distributed on the carbon support, and cobalt and nitrogen mainly overlap at the locations where platinum particles are distributed. From this, it can be inferred that platinum includes cobalt nitrides on its surface.

[0141] Based on the results of EDS line scan distribution map limited to a single particle ( Figure 12F It can be confirmed that the particles are mainly composed of platinum and cobalt nitrides included on the platinum surface.

[0142] Preparation Example 2 (CoN-Pt / CoNC-Bulk)

[0143] An aqueous solution obtained by dissolving the metal precursor Co(NO3)2·6H2O (3.1 mmol) in 6 ml of distilled water was supplied at a rate of 5 ml / h and mixed with an aqueous solution obtained by dissolving 2-methylimidazole (12.2 mmol) in 40 ml of distilled water. The mixture was stirred for 6 hours and then centrifuged and dried to synthesize a support (ZIF-67) with a polyhedral crystal structure.

[0144] In an inert gas (N2) atmosphere, the temperature of the support (2.0 g) was increased from 25 °C to 800 °C at a rate of 5 °C / min, and then heat-treated at 800 °C for 1 hour to form a carbon support (Co / CoNC-block) with cobalt non-precious metal particles on the surface and doped with nitrogen.

[0145] A carbon support (Co / CoNC-block) (0.1 g) was mixed with a platinum solution (40 μl, 1.93 M) in ethylene glycol solvent (EG, 40 ml). The pH was then adjusted to approximately 7 using an aqueous KOH solution. The mixture was stirred and heat-treated at 80 °C for 8 hours. After washing with distilled water and ethanol, the mixture was dried and dispersed in a 0.5 M aqueous hydrochloric acid solution. The mixture was then subjected to a hydrothermal reaction at 100 °C for 2 hours to remove pure cobalt non-precious metal particles from the surface of the carbon support. The mixture was then dried to prepare a carbon support with platinum particles attached to its surface.

[0146] Subsequently, a heat treatment was performed at 500°C for 30 minutes in an ammonia atmosphere to prepare an electrode catalyst (CoN-Pt / CoNC-block) comprising platinum particles containing cobalt nitrides attached to the surface and a nitrogen-doped carbon support.

[0147] Figure 13A TEM images of the electrode catalyst prepared above are shown. Figure 13B This image shows a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the electrode catalyst. Figures 13C to 13F The results of surface qualitative analysis using energy-dispersive X-ray spectroscopy (EDS) are shown.

[0148] Reference Figures 13A to 13F It can be confirmed that the electrode catalyst includes a support with a three-dimensional polyhedral crystal structure, and that platinum particles are distributed on the support, cobalt and nitrogen are uniformly distributed throughout the catalyst, and some cobalt and nitrogen overlap at the locations where the platinum particles are distributed, indicating that cobalt nitrides are formed on the platinum particles.

[0149] Preparation Example 3 (Pt / CoNC-2D)

[0150] An aqueous solution obtained by dissolving the metal precursor Co(NO3)2·6H2O (3.1 mmol) in 6 ml of distilled water was supplied at a rate of 5 ml / h and mixed with an aqueous solution obtained by dissolving 2-methylimidazole (12.2 mmol) in 40 ml of distilled water. The resulting mixture was stirred for 6 hours and then centrifuged and dried to synthesize a support with a polyhedral crystal structure (ZIF-67).

[0151] ZIF-67 (0.5 g) and cobalt nitrate hydrate Co(NO3)2·6H2O (1.0 g) were uniformly mixed in methanol and then hydrothermally reacted at 160 °C for 2 hours to convert the support into a two-dimensional planar crystal structure.

[0152] In an inert gas (N2) atmosphere, the temperature of a carrier (2.0 g) with a transformed crystal structure was increased from 25 °C to 800 °C at a rate of 5 °C / min, and then heat-treated at 800 °C for 1 hour to form a carbon carrier (Co / CoNC-2D) with cobalt non-noble metal particles on the surface and doped with nitrogen.

[0153] The carbon support thus obtained was washed with distilled water and ethanol and dried. It was then dispersed in a 0.5 M hydrochloric acid aqueous solution and subjected to a hydrothermal reaction at 100 °C for 2 hours to remove pure cobalt non-precious metal particles from the surface of the carbon support. It was then dried to obtain a carbon support without metal particles on the surface.

[0154] A carbon support (CoNC-2D) (0.1 g) was mixed with a platinum solution (40 μl, 1.93 M) in ethylene glycol solvent (EG, 40 ml), and the pH was adjusted to approximately 7 using an aqueous KOH solution. The mixture was then stirred and heat-treated at 140 °C for 8 hours to prepare an electrode catalyst (Pt / CoNC-2D) comprising a nitrogen-doped carbon support and platinum particles attached to the surface of the carbon support.

[0155] Figure 14A TEM images of the electrode catalyst prepared above are shown. Figure 14B This image shows a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image of the electrode catalyst. Figures 14C to 14G The results of surface qualitative analysis using energy-dispersive X-ray spectroscopy (EDS) are shown.

[0156] Reference Figures 14A to 14G It can be confirmed that the platinum particles are distributed on the carbon support, but cobalt and nitrogen are uniformly distributed throughout the carbon support, regardless of the distribution of the platinum particles.

[0157] Experimental Example (1)

[0158] The electrode catalysts prepared in Preparation Examples 1, 2, and 3 were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results are shown in... Figure 15 And in Table 1 below.

[0159] [Table 1]

[0160]

[0161]

[0162] Reference Figure 15 In Preparation Example 2, although the hydrothermal reaction was carried out in an aqueous hydrochloric acid solution, cobalt metal was still included on the carbon support, and the diffraction pattern of platinum was indistinguishable from the reference pattern, indicating that platinum and cobalt did not form an alloy but existed separately. In Preparation Examples 1 and 3, cobalt metal was not included on the carbon support, but the diffraction pattern of platinum was indistinguishable from the reference pattern, indicating that platinum existed separately. In particular, in Preparation Example 2, since platinum did not form an alloy with cobalt metal, but rather cobalt nitrides were distributed on the surface of platinum, the diffraction pattern of platinum remained unchanged.

[0163] Based on the results in Table 1, Preparation Example 1, in which platinum and cobalt nitride coexist, contained a significant amount of cobalt and nitrogen compared to Preparation Example 3, in which platinum particles existed alone. The high cobalt content in Preparation Example 2 is due to the accumulation of cobalt metal on polyhedral carbon; therefore, the cobalt metal particles did not react during the platinum loading process and the hydrothermal reaction in the hydrochloric acid aqueous solution, but remained on the carbon support.

[0164] Experimental Example (2)

[0165] The specific surface area of ​​the electrode catalysts prepared in Preparation Example 1 and Preparation Example 2 was measured. Figure 16A ) and the holes therein ( Figure 16B The results are shown in Figure 16A and Figure 16B middle.

[0166] Reference Figure 16A In Preparation Example 1 and Preparation Example 2, micropores and mesopores were present, and in Preparation Example 1, macropores were also present based on adsorption / desorption at a relative pressure of around 1.0. Therefore, the specific surface area of ​​Preparation Example 1 was 287.8 m². 2 / g, the specific surface area of ​​Preparation Example 2 is 202.3m². 2 / g.

[0167] Reference Figure 16B Preparation Example 1 included micropores with an average size of 1.2 μm (54.2 μm). 2The micropores consist of pores ranging from 0.6 to 2 nm (163.7 μm / g), mesopores with sizes from 4 to 50 μm, and macropores with sizes from 50 to 128 μm, with a micropore-to-specific surface area ratio of 19%. Preparation Example 2 included micropores with sizes from 0.6 to 2 nm (163.7 μm / g). 2 The surface area consists of micropores and a limited number of mesopores ( / g), with the ratio of micropores to specific surface area being 81%.

[0168] Experimental Example (3)

[0169] Compared to platinum catalysts (Pt / C) supported on carbon supports commonly used in fuel cells (hereinafter referred to as Comparative Example 1), in a three-electrode system (reference electrode: platinum wire; counter electrode: KCl-saturated Ag / AgCl; working electrode: Preparation Example 1, Preparation Example 2, Preparation Example 3, and Comparative Example 1), the activity of the electrode catalysts in Preparation Example 1, Preparation Example 2, and Preparation Example 3 as half of the fuel cell reaction was measured using oxygen-saturated 0.1M HClO4 electrolyte. The results are shown in... Figures 17A to 17F middle.

[0170] Figure 17A The linear sweep voltammetry (LSV) curves show the current density of the rotating disk at 1600 rpm in the presence of the catalyst in each of Preparation Examples 1 to 3 and Comparative Example 1. Figure 17B Tafel diagrams of preparation examples 1 and 3 are shown. Figure 17C It is a graph showing the amount of hydrogen peroxide (H2O2) produced and the number of electrons transferred per oxygen molecule in the oxygen reduction reaction, calculated from the current density of the rotating ring disk at 1600 rpm. Figure 17D , Figure 17E and Figure 17F The LSV curve shows the change in current density of the electrode catalysts of Preparation Example 1, Preparation Example 3 and Comparative Example 1 before and after the accelerated durability test (ADT) at 1600 rpm rotating ring disk.

[0171] based on Figure 17A The results, by comparing the initiation voltage (Einitial), half-wave voltage (E1 / 2), and threshold current density, show that the ORR activity of Preparation Example 1 is excellent. Based on Figure 17B As a result, in the kinetic region of the ORR catalyst reaction, Preparation Example 1 exhibited a Tafel slope of 49.5 mV / dec, which was smaller than that of Preparation Example 3 (65.8 mV / dec), thus enabling faster electron transfer. Based on Figure 17CAs a result, in Preparation Example 1, the number of electrons transferred during the catalytic reaction at 0.15 to 0.8 V was 3.99, and the amount of hydrogen peroxide produced by the 2-electron ORR reaction was less than 0.26%. Therefore, the 4-electron ORR reaction was the dominant catalytic reaction. Figure 17D , Figure 17E and Figure 17F The results confirmed the LSV change due to the performance degradation of the electrode catalyst after ADT. Preparation Example 1 was the most stable because the change in half-wave voltage (E1 / 2) was 17 mV in Preparation Example 1, 30 mV in Preparation Example 3, and 36 mV in Comparative Example 1.

[0172] This confirms that cobalt nitrides on the platinum surface improve ORR activity and stability.

[0173] Experimental Example (4)

[0174] Figure 18A and Figure 18B This is a graph showing the current-voltage polarization curves and power density of the oxygen reduction reaction (ORR) electrode at the cathode of the membrane electrode assembly of a fuel cell manufactured using the electrode catalysts of each of Preparation Example 1, Preparation Example 3 and Comparative Example 1, under hydrogen / oxygen fuel conditions, as well as the current per unit mass of platinum at 0.8V of the corresponding polarization curve.

[0175] In this experiment, the electrode catalyst of Comparative Example 1 was used as the anode, and in each evaluation, the platinum content in both the anode and cathode was 0.1 mg. pt / cm 2 NR211 was used as the electrolyte membrane. The current-voltage polarization curves and power density curves were determined under hydrogen and oxygen conditions at 0.5 bar.

[0176] based on Figure 18A As a result, the maximum electric power density in Preparation Example 1 was 1.33 W / cm². 2 In preparation example 3, the value was 1.24 W / cm. 2 In Comparative Example 1, it was 1.10 W / cm. 2 At 0.8V, the current per unit electrode area in Preparation Example 1 was 0.207 A / cm. 2 In Preparation Example 3, the value was 0.158 A / cm. 2 In Comparative Example 1, it was 0.130 A / cm. 2 This indicates that the prepared Example 1 exhibits excellent membrane electrode assembly activity. Based on Figure 18B As a result, Preparation Example 1 exhibited excellent current per unit mass of platinum at 0.8 V. This suggests that the cobalt nitride on the platinum surface enhances the ORR activity in the membrane electrode assembly.

[0177] Experimental Example (5)

[0178] Figure 19A , Figure 19B , Figure 19C and Figure 19D In the oxygen reduction reaction (ORR) electrode, which is the cathode of the membrane electrode assembly used in fuel cells and prepared using the electrode catalysts of Preparation Example 1 and Comparative Example 1, the electrode area per unit electrode area of ​​1 A cm² is measured under hydrogen / oxygen fuel conditions. -2 The graph shows the current variation over 100 hours, the current-voltage polarization curves during the initial stage and after 100 hours, the power density curves during the initial stage and after 100 hours, and the current per unit mass of platinum at 0.8V during the initial stage and after 100 hours.

[0179] In this experiment, the electrode catalyst of Comparative Example 1 was used as the anode, and in each evaluation, the platinum content in both the anode and cathode was 0.1 mg. pt / cm 2 NR211 was used as the electrolyte membrane. The current-voltage polarization curves and power density curves were determined under hydrogen and oxygen conditions at 0.5 bar.

[0180] like Figure 19A As shown, 1A / cm during 100 hours 2 The voltage decreased by 1.0% in Preparation Example 1 and by 6.7% in Comparative Example 1, indicating that Preparation Example 1 is more stable. Figure 19B As shown, the current per unit electrode area at 0.8V in Preparation Example 1 was 0.182 A / cm. 2 In Comparative Example 1, it was 0.088 A / cm. 2 And as Figure 19C As shown, the maximum electric power density in Preparation Example 1 was 1.31 W / cm². 2 In Comparative Example 1, it was 1.06 W / cm. 2 .like Figure 19D As shown, the area per unit electrode is 1 A / cm². 2 The rate of decrease in current per unit mass of platinum at 0.8V after 100 hours was 11.9% in Preparation Example 1 and 32.7% in Comparative Example 1, thus confirming that the cobalt nitride on the platinum surface improves the ORR stability in the membrane electrode assembly.

[0181] Although exemplary forms of this disclosure have been disclosed for illustrative purposes, those skilled in the art will understand that various modifications, additions, and substitutions may be made without departing from the scope and spirit of this disclosure.

Claims

1. A method for preparing a catalyst, comprising: Supports were prepared by synthesizing metal precursors and alkyl imidazoles; The carrier and cobalt nitrate hydrate were added to a solvent and subjected to a hydrothermal reaction. A carbon support is prepared by subjecting the support to a primary heat treatment. The carbon support is added to a solvent along with platinum, and the carbon support is subjected to a second heat treatment to load platinum and doped nitrogen on the surface of the carbon support. The carbon support is purified by removing one or more pure non-precious metal particles from the carbon support through acid treatment, wherein the non-precious metal particles attached to the platinum particles are retained; and The carbon support is subjected to three heat treatments, during which ammonia, together with non-noble metal particles formed on the surface of the platinum particles, synthesizes into nitrides. The synthesis includes: A first aqueous solution containing a dissolved metal precursor is provided, and this is mixed with a second aqueous solution of alkyl imidazole under stirring. The one or more pure non-precious metal particles include non-precious metal particles formed through initial heat treatment.

2. The method according to claim 1, wherein, The carrier comprises ZIF-67 as a zeolite imidazole ester backbone.

3. The method according to claim 1, wherein, The initial heat treatment is carried out in an inert gas atmosphere at a temperature of 25°C to 1000°C for 10 to 300 minutes, and the secondary heat treatment is carried out at a proton concentration below 7 (pH) at a temperature of 60°C to 100°C for 2 to 10 hours.

4. The method according to claim 1, wherein, The carrier after the initial heat treatment includes cobalt particles on its surface.

5. The method according to claim 1, wherein, The carbon support after undergoing secondary heat treatment comprises particles on its surface selected from the group consisting of cobalt, nickel, platinum, and combinations thereof.

6. The method according to claim 1, wherein, The acid treatment is carried out in an aqueous hydrochloric acid solution at a temperature of 90°C to 120°C for 1 to 3 hours.

7. The method according to claim 1, wherein, One or more pure non-precious metal particles removed from the carbon support by the acid treatment include pure cobalt that is not bonded to platinum.

8. The method according to claim 1, wherein, The three heat treatments are carried out in an ammonia atmosphere at a temperature of 300°C to 600°C for 10 to 60 minutes.

9. A catalyst prepared by the method according to any one of claims 1-8, comprising: Carbon support, doped with nitrogen; as well as Solid particles, loaded on the surface of the carbon support. The solid particles include noble metal particles and noble metal particles containing nitrides. The carbon support has a two-dimensional planar crystal structure and a thickness of 10 nm to 200 nm. The precious metal particles include platinum.

10. The catalyst according to claim 9, wherein, The porosity of the carbon support is 10% to 85%.

11. The catalyst according to claim 9, wherein, The nitrogen-containing noble metal particles include cobalt nitrides.

12. The catalyst according to claim 9, wherein, The catalyst is contained in the electrodes of a fuel cell or a water electrolysis cell.

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