Catalyst electrode for anion exchange membrane water electrolysis or fuel cells and manufacturing method therefor

Abstract

Disclosed is a catalyst for a hydrogen evolution reaction or a hydrogen oxidation reaction, which can be used under alkaline conditions and has significantly improved kinetic properties compared to conventional commercially-available platinum catalysts. The present invention provides a catalyst for electrochemical hydrogen reactions under alkaline conditions, which has 2 to 20 ruthenium atoms supported in an ensemble form on the surface of a molybdenum carbide-carbon nanocomposite support, and a manufacturing method therefor, and a ruthenium-based catalyst electrode comprising the catalyst, which can be used as an electrode for anion exchange membrane-based water electrolysis cells and fuel cells.

Description

Anion exchange membrane catalytic electrode for water electrolysis or fuel cell and method for manufacturing the same

[0001] The present invention relates to a catalyst electrode for electrolysis or a fuel cell and a method for manufacturing the same, and more particularly, to an anion exchange membrane catalyst electrode for electrolysis or a fuel cell and a method for manufacturing the same.

[0002] This application claims priority to and the benefit of Republic of Korea Patent Application No. 10-2023-0171746, filed November 30, 2023, which is incorporated herein by reference in its entirety.

[0003] Electrolysis technology produces hydrogen using renewable energy-based electrical energy. This eco-friendly technology allows surplus electricity to be stored as hydrogen or used in processes such as oil refining and ammonia production. Fuel cell technology converts hydrogen into electrical energy, allowing the stored energy to be utilized where needed. For these two electrochemical conversion devices, the operating environment and characteristics depend on the electrolyte membrane used. Currently, cation exchange membrane-based devices are closest to commercialization. However, cation exchange membrane-based devices operate under strongly acidic conditions, necessitating the use of large quantities of precious metals in the oxygen electrode. In contrast, anion exchange membrane-based devices operate under strongly alkaline conditions. Under alkaline conditions, the kinetics of the electrochemical oxygen reaction are very rapid, and non-precious metal catalysts can react stably. Consequently, non-precious metal catalysts can be used in the oxygen electrode. Therefore, the cost of catalysts, which account for a large portion of the conversion device price, can be significantly reduced, ensuring high economic efficiency. In other words, anion exchange membrane-based conversion devices are a highly commercially viable technology that can overcome the price limitations of existing cation exchange membrane conversion devices.

[0004] However, the electrochemical hydrogenation reaction under strongly alkaline conditions has significantly lower kinetic performance of commercial platinum catalysts than under strongly acidic conditions, which reduces the efficiency of anion exchange membrane-based converters and limits their commercialization. Since electrochemical hydrogenation under strongly alkaline conditions inevitably requires the use of precious metals, the development of noble metal-based catalysts that reduce the amount of precious metals used while also exhibiting high performance and stability in the hydrogenation reaction under strongly alkaline conditions is essential for the commercialization of anion exchange membrane-based converters.

[0005] Meanwhile, research on single-atom catalysts with structures that maximize precious metal utilization to lower catalyst costs has been actively conducted recently. Single-atom synthesis primarily relies on low-metal loading, low-temperature synthesis methods to prevent sintering between metal atoms with atomic-scale structures. However, these catalysts suffer from low active site density due to the limitations of these synthesis methods. Furthermore, the inability to form strong chemical bonds between the metal and the support at low temperatures results in low stability, hindering their application to membrane-electrode assemblies (MEAs) used in practical conversion devices.

[0006] The present invention provides a catalyst for hydrogen production or hydrogen oxidation reaction that can be used under basic conditions, and has significantly improved kinetic characteristics compared to existing commercial platinum catalysts, and a method for producing the same, and a ruthenium-based catalyst electrode that can be used as an electrode for an anion exchange membrane-based water electrolysis cell and a fuel cell including the catalyst.

[0007] To solve the above problem, the present invention provides a catalyst for electrochemical hydrogenation under basic conditions, in which 2 to 20 ruthenium atoms are supported in an ensemble form on the surface of a molybdenum carbide-carbon nanocomposite support.

[0008] In addition, the ensemble of rutheniums interconnected with each other provides a catalyst for electrochemical hydrogenation under basic conditions, characterized in that the ruthenium has a two-dimensional structure exposed on the surface of the molybdenum carbide-carbon nanocomposite support.

[0009] In addition, the present invention provides a catalyst for electrochemical hydrogenation under basic conditions, characterized in that the ruthenium is contained in an amount of 1 to 15 wt% of the entire catalyst.

[0010] In addition, the molybdenum carbide-carbon nanocomposite support provides a catalyst for electrochemical hydrogenation under basic conditions, characterized by a porous structure.

[0011] In addition, the present invention provides a catalyst for an electrochemical hydrogen reaction, characterized in that the electrochemical hydrogen reaction is a hydrogen production reaction or a hydrogen oxidation reaction.

[0012] In addition, a catalyst electrode for an anion exchange membrane electrolysis or fuel cell including the above catalyst is provided.

[0013] In order to solve the above other problems, the present invention provides a method for preparing the catalyst comprising the following steps.

[0014] (A) A step of mixing a ruthenium precursor and a molybdenum precursor into a solution containing a carbon precursor;

[0015] (B) a step of evaporating the solvent of the mixed solution to form a film;

[0016] (C) a step of micronizing the film after the first heat treatment; and

[0017] (D) A step of performing a second heat treatment on the above undifferentiated catalyst.

[0018] In addition, a method for preparing a catalyst is provided, characterized in that the ruthenium precursor is ruthenium acetylacetonate.

[0019] In addition, the present invention provides a method for manufacturing a catalyst, characterized in that the carbon precursor is poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS), phenol-formaldehyde resin (PF resin) or melamine-formaldehyde resin (MF resin), and the molybdenum precursor is phosphomolybdic acid.

[0020] In addition, a catalyst manufacturing method is provided, characterized in that the first heat treatment is performed at 80 to 200°C, and the second heat treatment includes the following steps.

[0021] (D1) A step of introducing the above-mentioned undifferentiated catalyst into a tubular kiln, heat-treating it at 300 to 600°C for 1 to 10 hours in an argon gas flow and at 700 to 1,000°C for 2 to 15 hours, then cooling it to room temperature and maintaining it in a mixed gas flow of oxygen and argon for 5 to 30 hours to passivate it and then undifferentiating it;

[0022] (D2) A step of heat-treating the powder obtained in the step (D1) at 100 to 200°C for 2 to 15 hours in a mixed gas flow of oxygen and argon, and then cooling to room temperature to finely differentiate it; and

[0023] (D3) A step of heat-treating the powder obtained in the above step (D2) in an argon gas flow at a temperature of 700 to 2,000°C for 2 to 15 hours, cooling to room temperature, and maintaining the powder in a mixed gas flow of oxygen and argon for 5 to 30 hours to passivate it, and then finely pulverize it.

[0024] The present invention is a catalyst in which ruthenium is supported in an ensemble form in an atomic-scale structure on the surface of a molybdenum carbide-carbon nanocomposite support in which molybdenum carbide is embedded on a carbon skeleton, and when applied to an electrochemical hydrogenation reaction under strong alkaline conditions, it can exhibit kinetic characteristics approximately four times superior to those of a commercial platinum catalyst.

[0025] Figures 1a to 1g are photographs showing the results of STEM (scanning transmission electron microscopy), EDX (energy-dispersive X-ray) mapping, and SEM (scanning electron microscope) analysis of the catalyst manufactured in Test Example 2.

[0026] Figures 2a to 2d are graphs showing the results of XANES (X-ray Absorption Near Edge Structure) and FT-EXAFS (Fourier-transformed Extended X-ray Absorption Fine Structure) analysis for the catalyst manufactured in Test Example 3.

[0027] Figures 3a to 3g are graphs showing the results of tests on the performance and stability of hydrogen evolution reaction (HER) under strong alkaline conditions, the performance of hydrogen oxidation reaction (HOR), and the application to a membrane-electrode assembly (MEA) of the catalyst manufactured in Test Example 4.

[0028] Hereinafter, the present invention will be described in detail through preferred embodiments. Prior to this, it should be noted that the terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted as meanings and concepts that conform to the technical concept of the present invention. Therefore, the configuration of the embodiments described in this specification is only the most preferred embodiment of the present invention and does not represent the entire technical concept of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of filing this application.

[0029]

[0030] The present invention discloses a catalyst for electrochemical hydrogenation under basic conditions, wherein 2 to 20 ruthenium atoms are supported in an ensemble form on the surface of a molybdenum carbide-carbon nanocomposite support.

[0031] In the present invention, the ruthenium supported in an ensemble form is supported in an ensemble form in which 2 to 20 ruthenium atoms are connected to each other in an atomic scale structure on the surface of a molybdenum carbide-carbon nanocomposite support in which molybdenum carbide is embedded on a carbon skeleton.

[0032] The catalyst according to the present invention is a catalyst for hydrogen production reaction or hydrogen oxidation reaction under basic conditions, and is composed of a ruthenium ensemble-porous molybdenum carbide / carbon nanocomposite utilizing molecular interactions between metal precursors, and is applied as an electrode catalyst for anion exchange membrane-based water electrolysis cells and fuel cells.

[0033] In the present invention, the ruthenium is derived from a specific precursor. That is, by selecting ruthenium acetylacetonate as a ruthenium precursor and using it in the synthesis, the synthesis of a ruthenium ensemble catalyst supported on a porous molybdenum carbide / carbon nanocomposite with various ruthenium loading amounts can be realized by utilizing the molecular interaction between metal precursors.

[0034] Here, in the case of conventional ruthenium precursors such as ruthenium chloride, the interaction between ruthenium precursors is too strong and the absence of interaction between the ruthenium precursor and the molybdenum precursor leads to the formation of a large number of ruthenium agglomerates, which significantly reduces the utilization of ruthenium and significantly reduces the electrochemical performance per noble metal.

[0035] In this regard, according to the present invention, when ruthenium acetylacetonate is used as a ruthenium precursor, ruthenium chemical species can be uniformly dispersed on a support without large-sized ruthenium agglomerates through interaction with phosphomolybdic acid, a molybdenum precursor, thereby easily synthesizing a ruthenium ensemble catalyst having an atomic-scale structure despite a high loading amount.

[0036] At this time, the ruthenium ensemble is a form in which 2 to 20 ruthenium atoms, preferably 2 to 10 ruthenium atoms, are connected to each other in an atomic scale structure. In the present invention, the ruthenium ensemble is selectively supported on the molybdenum carbide, and can form a two-dimensional structure exposed on the surface of the molybdenum carbide-carbon nanocomposite support.

[0037] The selective loading and two-dimensional structure formation of the ruthenium ensemble is achieved by selecting a specific molybdenum compound as a support and applying a high-temperature synthesis method rather than a conventional low-temperature synthesis method. That is, in the present invention, a molybdenum carbide-carbon nanocomposite in which molybdenum carbide is embedded on a porous carbon skeleton (mesoporous structure) as a support is applied, and a high-temperature synthesis method is applied, thereby implementing a strong interaction between the ruthenium catalyst and the molybdenum support, so that the ruthenium ensemble is selectively loaded on the molybdenum carbide, and through the strong metal-support interaction (SMSI), the utilization of ruthenium is maximized, while at the same time, the stability in electrochemical catalytic reactions is greatly improved.

[0038] The above molybdenum carbide has a high affinity for noble metal species and can stabilize ruthenium species in an atomic-scale structure under high-temperature synthetic conditions, thereby allowing the ruthenium species to have an ensemble form of a two-dimensional structure (2D structure) rather than a cluster form of a three-dimensional structure (3D structure), thereby maximizing the utilization of ruthenium and optimizing the electrochemical hydrogen reaction performance.

[0039] Here, in the case of particle-based catalysts having a conventional three-dimensional structure, only some elements exposed on the surface are utilized as active sites, but in the case of the ensemble catalyst synthesized according to the present invention, since it has a two-dimensional structure, all ruthenium chemical species are exposed on the surface, so all ruthenium elements can be utilized, thereby maximizing the utilization of precious metals and significantly reducing the amount of precious metals used. Specifically, in the present invention, ruthenium (Ru), which is priced at about 1 / 3 of platinum, is utilized instead of platinum (Pt), which is generally used in hydrogen reactions, so it is very advantageous in terms of commercialization, and in particular, molybdenum carbide greatly stabilizes the ruthenium ensemble (Ru ensemble) through a high-temperature synthesis method, thereby exhibiting significantly improved electrochemical stability compared to conventional catalysts.

[0040] In this way, the present invention implements a ruthenium ensemble-molybdenum carbide interface system through the strong interaction between the ruthenium ensemble and molybdenum carbide, and by applying this interface system to an electrochemical hydrogenation reaction under strongly alkaline conditions, it achieves a kinetic performance that is significantly improved by more than four times compared to existing platinum or ruthenium-based catalysts, thereby significantly improving the commerciality of an anion exchange membrane-based conversion device through the improvement of kinetic performance while reducing the catalyst price.

[0041] Specifically, in the electrochemical hydrogenation reaction under strongly basic conditions, the high activation energy for the water splitting reaction results in a significantly lower kinetic performance for commercial platinum catalysts compared to strongly acidic conditions. In contrast, the molybdenum carbide support significantly lowers the activation energy for the water splitting reaction, thereby significantly improving the kinetic characteristics of the electrochemical hydrogenation reaction occurring at the surrounding ruthenium active sites. At the same time, the catalyst according to the present invention can overcome the limitations of existing single-atom catalysts by dispersing ruthenium not as a single atom but in an ensemble form in which two or more ruthenium species are connected to each other.

[0042] At this time, since the adsorption energy for the reactant changes depending on the size or amount of the ruthenium ensemble, the present invention predicted that there would be an ideal ensemble size or amount that could dramatically improve the performance per precious metal, and through experiments, it was confirmed that the most ideal performance improvement was shown when ruthenium was contained in an amount of 1 to 15% by weight of the entire catalyst, preferably 2 to 10% by weight, and more preferably 3 to 8% by weight.

[0043] As described above, the catalyst according to the present invention exhibits performance superior to that of existing commercial platinum catalysts when applied to an anion exchange membrane-based conversion device, and the ruthenium ensemble catalyst presented through a high-temperature synthesis method exhibits performance far superior to that of existing commercial platinum catalysts in application to actual membrane electrode assemblies (MEAs), which existing single atoms have not been able to demonstrate, due to significantly improved active site density, kinetic performance, and stability.

[0044] Hereinafter, a method for manufacturing a catalyst for a hydrogen production reaction or hydrogen oxidation reaction under basic conditions according to the present invention will be described in detail.

[0045] The method for producing a catalyst for a hydrogen production reaction or hydrogen oxidation reaction under basic conditions according to the present invention comprises the steps of (A) mixing a ruthenium precursor and a molybdenum precursor in a solution containing a carbon precursor; (B) evaporating a solvent of the mixed solution to produce a film; (C) subjecting the film to a first heat treatment and then pulverizing it; and (D) subjecting the pulverized catalyst to a second heat treatment.

[0046] In the present invention, by synthesizing a catalyst using a modified interaction mediator assisted evaporation-induced self-assembly (IM-EISA) method that involves (A) precursor mixing, (B) film formation, (C) first heat treatment followed by micronization, and (D) second heat treatment, it was confirmed that it is possible to manufacture a catalyst for hydrogen production or hydrogen oxidation with significantly improved kinetic properties.

[0047] As mentioned above, it is preferable to use ruthenium acetylacetonate as the ruthenium precursor and phosphomolybdic acid as the molybdenum precursor.

[0048] In the above step (A), a ruthenium precursor and a molybdenum precursor are mixed into a solution containing a carbon precursor to prepare a precursor solution. The carbon precursor may be a block copolymer or an organic polymer. The block copolymer is not particularly limited as long as it is a material that introduces a porous structure into a carbon skeleton through self-assembly of the synthesized molybdenum carbide while evenly dispersing metal chemical species on the carbon skeleton. For example, it may be poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS). When PEO-b-PS is mixed with a molybdenum precursor at a specific ratio, the molybdenum precursor has a strong interaction with the PEO block and is selectively positioned. In addition, the organic polymer is not particularly limited as long as it is a material that forms a carbon skeleton and is used as a carbon source for carbonization of a molybdenum precursor, and for example, it may be a phenol-formaldehyde resin (PF resin) or a melamine-formaldehyde resin (MF resin), and when it undergoes a subsequent heat treatment process, a stable nanostructure is formed through crosslinking.

[0049] Specifically, in the case of the organic polymer, it stabilizes the porous structure formed through cross-linking during the first heat treatment and is utilized as a carbon source for the carbon skeleton and the carbonization process of molybdenum. In addition, during the second heat treatment process, the cross-linked organic polymer is converted into a carbon skeleton, and the molybdenum precursor decomposes at the same time, and molybdenum carbide is formed through a reaction with the carbon skeleton, and the molybdenum carbide nanoparticles are stabilized due to the carbon skeleton and do not grow large. In addition, in the case of the MF resin, it improves the interaction between the molybdenum precursor and the block copolymer as an interaction mediator and a carbon source, so that molybdenum carbide can be formed into small nanoparticles.

[0050] At this time, by applying ultrasonic treatment and stirring to the precursor solution, the precursors can be completely dissolved in a solvent such as tetrahydrofuran (THF) for self-assembly.

[0051] In the above step (B), the solvent is evaporated from the mixed solution of the above step (A) to form a film, and in the above step (C), the formed film is subjected to a first heat treatment and then finely divided. The above first heat treatment step may be performed at 80 to 200°C, preferably at 90 to 150°C for 12 to 84 hours, and more preferably at 90 to 120°C for 24 to 72 hours.

[0052] The above step (D) is a step of obtaining a final catalyst through three consecutive heat treatment processes on the powder obtained through the first heat treatment.

[0053] Specifically, the step (D) is a step (D1) of putting the undifferentiated catalyst into a tube furnace, heat-treating it in an argon gas flow at a temperature of 300 to 600°C for 1 to 10 hours and at a temperature of 700 to 1,000°C for 2 to 15 hours, cooling it to room temperature, maintaining it in an oxygen and argon mixed gas flow for 5 to 30 hours to passivate it, and then undifferentiating it (first heat treatment); (D2) a step of undifferentiating the undifferentiated catalyst obtained in the step (D1) by heat-treating it in an oxygen and argon mixed gas flow at a temperature of 100 to 200°C for 2 to 15 hours, and then cooling it to room temperature; And (D3) a step (3rd heat treatment) may be included in which the powder obtained in the step (D2) is heat-treated in an argon gas flow at a temperature of 700 to 2,000°C for 2 to 15 hours, cooled to room temperature, and maintained in a mixed gas flow of oxygen and argon for 5 to 30 hours to passivate and then powderize.

[0054] In the first heat treatment, the initial flow rate of argon (Ar) may be 50 to 500 sccm, preferably 100 to 300 sccm. In addition, in the case of continuous heat treatment, the heat treatment may be performed at 400 to 500°C for 2 to 5 hours and at 800 to 900°C for 4 to 8 hours. Thereafter, after cooling to room temperature, the flow rates of the oxygen (O2) and argon (Ar) mixed gas may be 0.1 to 10 sccm and 50 to 500 sccm, respectively, preferably 0.5 to 5 sccm and 100 to 300 sccm, and the treatment time may be preferably 5 to 30 hours.

[0055] In addition, in the secondary heat treatment, the flow rates of the oxygen (O2) and argon (Ar) mixed gas may be 5 to 50 sccm and 10 to 200 sccm, respectively, and preferably 10 to 30 sccm and 50 to 100 sccm, and the heat treatment may be preferably performed at 110 to 150°C for 3 to 10 hours.

[0056] In the above third heat treatment, the initial flow rate of argon (Ar) may be 50 to 500 sccm, preferably 100 to 300 sccm. In addition, the heat treatment may be preferably performed at 800 to 1,500°C for 3 to 10 hours. Thereafter, after cooling to room temperature, the flow rates of the oxygen (O2) and argon (Ar) mixed gas may be 0.1 to 10 sccm and 50 to 500 sccm, respectively, preferably 0.5 to 5 sccm and 100 to 300 sccm, and the treatment time may be preferably 5 to 30 hours.

[0057] Hereinafter, specific examples according to the present invention will be described.

[0058]

[0059] Examples and Comparative Examples

[0060] (1) Preparation of ruthenium precursor solution

[0061] Ruthenium(III) acetylacetonate (Ru(acac)3) was dissolved in tetrahydrofuran (THF) solution and used as follows depending on the ruthenium ratio to be manufactured:

[0062] - aRu1 / Mo x C: 5 mL THF + 21.8 mg Ru(acac)3

[0063] - aRu2 / Mo x C: 5 mL THF + 43.7 mg Ru(acac)3

[0064] -aRu3 / Mo xC: 5 mL THF + 65.5 mg Ru(acac)3

[0065] - aRu4 / Mo x C: 5 mL THF + 87.3 mg Ru(acac)3

[0066] - aRu5 / Mo x C: 5 mL THF + 131.0 mg Ru(acac)3

[0067] (aRu# / Mo x In C, 'a' stands for 'atomically dispersed' or 'atom-dimension structured'.)

[0068] Also, as a comparative example, Ru / Mo x For the production of C_Cl, ruthenium(III) chloride hydrate was used as follows:

[0069] -Ru / Mo x C_Cl: 5 mL THF + 74.1 mg RuCl3·xH2O

[0070]

[0071] (2) Preparation of catalyst

[0072] The catalyst was synthesized using a modified interaction mediator assisted evaporation-induced self-assembly (IM-EISA) method.

[0073] First, 0.1 g of phenol-formaldehyde resin (PF resin), 0.02 g of melamine-formaldehyde resin (MF resin) and 0.2 g of PEO-b-PS (Mn = 50 kg mol -1, 10.0 wt% PEO, polydispersity = 1.25) was dissolved in 25 mL of THF, and the mixture was stirred at room temperature for 2 hours to become a transparent solution. Subsequently, a ruthenium precursor solution was added to the mixed solution, and the mixture was mixed by stirring for 10 minutes. After that, 0.2 g of PMA (Phosphmolybdic acid) was added to the mixed solution, sonicated for 30 minutes, and stirred for 30 minutes to completely dissolve it. Subsequently, the mixed solution was slowly evaporated of the solvent at 50°C for 12 hours. The film thus produced was additionally heat-treated at 100°C for 48 hours. Thereafter, the obtained film was pulverized for 10 minutes to become fine. Thereafter, the catalyst was obtained through three consecutive heat treatment processes as follows.

[0074] (i) Primary heat treatment: The powder obtained by the above-mentioned micronization was placed in a tube furnace, maintained at 450°C for 3 hours (heating rate: 1°C / min) while flowing argon (Ar, 200 sccm), then heat-treated at 850°C for 6 hours (heating rate: 5°C / min), and then cooled to room temperature (cooling rate: 5°C / min). After reaching room temperature, the sample was passivated for 24 hours in a mixed gas flow of oxygen (O2, 2 sccm) / argon (Ar, 200 sccm). Thereafter, the obtained powder was further pulverized for 10 minutes to micronize it.

[0075] (ⅱ) Secondary heat treatment: The powder obtained through the first heat treatment was treated in a tube furnace at 130°C for 6 hours (heating rate: 2°C / min) in a flow of oxygen (O2, 20 sccm) / argon (Ar, 80 sccm) mixed gas (= 20 vol% O2 / Ar), and then cooled to room temperature (cooling rate: 2°C / min). Thereafter, it was pulverized for 10 minutes to be finely divided.

[0076] (ⅲ) Third (final) heat treatment: The powder obtained through the second heat treatment in a tube furnace was heat treated at 1,100°C for 6 hours (heating rate: 5°C / min) in an argon (Ar, 200 sccm) flow, and then cooled to room temperature (cooling rate: 5°C / min). After reaching room temperature, the sample was passivated for 24 hours in a mixed gas flow of oxygen (O2, 2 sccm) / argon (Ar, 200 sccm). Afterwards, it was pulverized for 10 minutes to be finely divided.

[0077] Through the above process, the catalyst aRu# / Mo is finally obtained. x C was obtained. Here, in the case of the catalyst according to the present invention using ruthenium acetylacetonate, aRu# / Mo x It is denoted as C, and in the case of a catalyst using ruthenium chloride as a comparative example, Ru / Mo x It is expressed as C_Cl. The higher the ruthenium content, the larger the number of # is expressed.

[0078]

[0079] Test Example 1

[0080] The ruthenium content in the catalyst manufactured above was measured according to the following method, and the results are shown in Table 1 below.

[0081] [measurement method]

[0082] The catalyst was placed in aqua regia and dissolved through microwave reaction. The average value of five measurements was used using ICP-MS 7700S (Agilent).

[0083]

[0084] ClassificationRu content (wt%)Mo x C0aRu1 / Mo x C2.85aRu2 / Mo x C4.95aRu3 / Mo xC8.03aRu4 / Mo x C10.69aRu5 / Mo x C14.52Ru / Mo x C_Cl9.26

[0085]

[0086] Test Example 2

[0087] STEM (scanning transmission electron microscopy), EDX (energy-dispersive X-ray) mapping, and SEM (scanning electron microscope) analyses were performed on the above-mentioned manufactured catalyst according to the following methods, and the results are shown in FIGS. 1a to 1g.

[0088] [STEM, EDX mapping, and SEM analysis methods]

[0089] For STEM and EDX mapping, measurements were performed using a Tecnai G2 F30 S-Twin (FEI) equipment at an acceleration voltage of 300 kV, and for SEM, measurements were performed using a SU8230 (Hitachi) equipment.

[0090]

[0091] Referring to Figures 1a to 1g, all catalysts synthesized through the self-assembly strategy have a porous structure, and it can be confirmed that the molybdenum carbide nanoparticle support is evenly dispersed (embedded) on the carbon skeleton. In addition, referring to the STEM EDX mapping results, aRu# / Mo using ruthenium acetylacetonate x In the case of the C catalyst, it can be confirmed that ruthenium agglomerates do not exist, and that they are selectively and evenly dispersed with an atomic-scale structure only on the molybdenum carbide support. In contrast, Ru / Mo using ruthenium chloride xIn the case of the C_Cl catalyst, it can be predicted that very large (~100 nm) Ru agglomerates will be formed, which will significantly reduce the utilization of the precious metal of the catalyst. That is, by applying the ruthenium acetylacetonate according to the present invention to the self-assembly process, it is possible to interact with the molybdenum precursor, phosphomolybdic acid, so that it is stabilized at the level of several (less than 10) at the precursor level, and through the high-temperature synthesis process, it is selectively stabilized at the atomic-scale structure level on the molybdenum carbide support, as shown in FIGS. 1a to 1g. However, in the case of ruthenium chloride, stabilization by molecular interaction is impossible, so it can be seen that large agglomerates are formed, as shown in FIGS. 1a to 1g.

[0092]

[0093] Test Example 3

[0094] XANES (X-ray Absorption Near Edge Structure) and FT-EXAFS (Fourier-transformed Extended X-ray Absorption Fine Structure) analyses were performed on the above-mentioned manufactured catalyst according to the following methods, and the results are shown in Figs. 2a to 2d. For comparison, the results for ruthenium dioxide (RuO2) and ruthenium foil (Ru foil) are also shown.

[0095] [XANES and FT-EXAFS analysis methods]

[0096] Ru K-edge analysis was performed using the 8C Nano XAFS beamline at Pohang Accelerator Laboratory (PAL) to obtain X-ray absorption spectroscopy (XAS) data, including XANES and FT-EXAFS.

[0097]

[0098] Referring to FIGS. 2a to 2d, the catalyst (aRu2 / Mo) according to the present invention x In the case of C), a strong chemical bond is formed with the molybdenum carbide support through a high-temperature synthesis process, and SMSI is realized. In the case of the molybdenum carbide support, it is a support having a metallic character, and most single-atom catalysts are stabilized by elements or ligands such as oxygen (O), nitrogen (N), sulfur (S), etc., or are stabilized on a support having a non-metallic character such as oxide, so that it generally has a high oxidation number, unlike the catalyst according to the present invention (aRu# / Mo x In case C), the Ru ensemble catalyst has an oxidation number close to that of Ru foil, unlike the existing single atoms, due to the strong interaction with the metallic support, molybdenum carbide, which is evidence showing that SMSI can be implemented through the strategy according to the present invention.

[0099] Also, referring to the FT-EXAFS results, the catalyst according to the present invention (aRu# / Mo xIn the case of C), it is stabilized into an atomic-scale structure through Ru-C chemical bonding, and it can be confirmed that as the number of # increases, the height corresponding to the Ru-Ru chemical bonding increases, and from this, it is confirmed that the ensemble size of the sub-nano ruthenium cluster can be controlled by controlling the amount of ruthenium precursor. In addition, ruthenium foil (Ru foil) and Ru / Mo x From the very low Ru-Ru shell height compared to C_Cl, it can be confirmed that the Ru-Ru chemical bond corresponds to a 2D ensemble structure.

[0100]

[0101] Test Example 4

[0102] For the catalyst manufactured above, hydrogen evolution reaction (HER) performance and stability under strongly alkaline conditions, hydrogen oxidation reaction (HOR) performance, and application to a membrane electrode assembly (MEA) were tested according to the following method, and the results are shown in Figs. 3a to 3g. For comparison, the results for existing commercial platinum catalysts (Pt / C) and ruthenium catalysts (Ru / C) are also shown. For the commercial platinum catalyst (Pt / C), HISPEC 3,000 (Johnson Matthey Co.) was used, and for the Ru / C catalyst, the one prepared through the following chemical reduction method was used: 167.3 mg of RuCl3·xH2O was dissolved in 60 mL of anhydrous ethanol (10 min sonication & 1 hr stirring), 0.3 g of commercial carbon (Vulcan XC-72R) was added, dispersed (10 min sonication), and stirred. Then, a solution of 0.6 g of NaBH4 dissolved in 50 mL of anhydrous ethanol was added dropwise, slowly mixed into the above mixed solution, and the catalyst was obtained through vacuum filtration.

[0103] [HER, Stability, HOR, and MEA Test Methods]

[0104] <Electrochemical Characterization>

[0105] Electrochemical half-cell measurements were performed in a three-electrode system using a potentiostat (Reference 600, Gamry Instruments). A Hg / HgO electrode immersed in 1 M NaOH solution was used as the reference electrode. A graphite rod was used as the counter electrode. In addition, a 5 mm glassy carbon rotating disk electrode (RDE) was used as the substrate for the catalyst ink. The RDE was sequentially ground and polished with 0.3 μm and 0.05 μm alumina suspension before depositing the catalyst ink. Before preparing the catalyst ink, 40 mg of Vulcan XC 72 R was dispersed in 20 mL of isopropyl alcohol (IPA / C) by sonication for 20 min. To prepare catalyst ink, 15.3, 8.8, 5.4, 4.1, 3.0 mg of aRuX / MoxC (X=1,2,3,4,5, respectively) were dispersed in 400 ㎕ of distilled water containing 76, 44, 27, 20, 15 ㎕ of Sustainion® XA-9 Alkaline Ionomer (X=1,2,3,4,5) and 1600 ㎕ of IPA / C solution by ultrasonication for more than 1 hour. The ink of Pt / C catalyst was prepared using 2.2 mg of Pt / C catalyst, 389 ㎕ of distilled water, 11 ㎕ Sustainion® Xa-9 Alkaline Ionomer, and 1600 ㎕ of IPA / C solvent. The ink of Ru / C catalyst was prepared using 2.8 mg catalyst, 386 μl distilled water, 14 μl Sustaionion XA-9 Alkaline Ionomer and 1600 μl IPA / C solvent.

[0106] After that, 12 μl of catalyst ink was dropped on the RDE and the electrode was dried by rotating at 400 rpm, and the loading was repeated three times to make the electrode evenly, and thus the loading of Ru was 0.040 mg cm-2 (Pt / C is Pt loading of 0.042 mg cm -2 ) was prepared as a target electrode. Before conducting an electrochemical experiment, the cell and bubbler made of PTFE (Polytetrafluoroethylene) were soaked at 60°C for more than 1 hour to remove impurities. Afterwards, the voltage was calibrated by measuring in a H2-saturated 1.0 M KOH solution and expressed as RHE (Reversible hydrogen electrode).

[0107] In addition, before proceeding with the measurement, the electrode surface was activated by electrochemically cleaning it by running CV (Cyclic voltammetry) 40 times from -600 to 600 mV at 100 mV / s at 1600 rpm. The polarization curve was measured using LSV (Linear sweep voltammetry) at 1 mV / s at 1600 rpm, and iR correction was performed to eliminate the influence of the capacitive current. At this time, the HER polarization curve was measured from 20 mV to -300 mV, and the HOR polarization curve was measured from -20 mV to 150 mV. The HER Tafel plot was expressed using the following mathematical formula 1, and the HER durability (stability) test was performed at 1600 rpm and -20 mA cm -2 It was performed using CP (chronopotentiometry) for 24 hours under conditions.

[0108] <Mathematical Formula 1>

[0109]

[0110] In mathematical equation 1, η is the overpotential and j is the current density.

[0111] The HER polarization curve and HOR polarization curve in FIGS. 3a to 3g are shown in FIGS. 3a and 3b, respectively, the mass activity measurement results are shown in FIGS. 3c and 3d, the HER Tafel plot results are shown in FIG. 3e, and the HER durability (stability) test results are shown in FIG. 3f.

[0112] <AEMWE(Anion Exchange Membrane Water Electrolyzer) Measurements>

[0113] The membrane electrode assembly (MEA) was manufactured by placing a 20 micron PiperION® Anion Exchange Membrane, a self-supporting membrane, between the anode (oxidation electrode) and cathode (reduction electrode). The geometric active area of ​​the MEA was 1 cm 2 The prepared aRu2 / MoxC catalyst was used as a cathode catalyst, and 0.2 mgRu cm was applied to a carbon fiber electrode (Sigracet 39BB). -2 was manufactured by spray coating. In addition, NiFe catalyst was used as an anode catalyst, and 3.0 mg cm was applied to SUS electrode (SS Fiber Paper). -2was prepared by spray coating. The aRu2 / MoxC catalyst ink was prepared using 50 mg of aRu2 / MoxC catalyst, 0.75 mL of distilled water, 0.75 mL of absolute ethanol, 1.5 mL of IPA, and 98.2 mL of 5 wt% PiperION® Anion Exchange Dispersion, and the NiFe catalyst was prepared using 60 mg of catalyst, 0.9 mL of distilled water, 0.9 mL of absolute ethanol, 1.8 mL of IPA, and 161.4 mL of 5 wt% PiperION® Anion Exchange Dispersion, and each was dispersed through sonication for more than 3 hours. After that, the electrodes were fabricated using spray coating, and both the electrodes and the membrane were soaked in 1.0 M KOH for more than 24 hours for anion dispersion and pre-activation of the anion exchange membrane, respectively, and then washed with distilled water to fabricate a cell.

[0114] The single-cell test was performed using a potentiostatic method in the range of 1.35 to 2.10 Vcell at 0.05 V intervals for 2 minutes while controlling the temperature (60 to 90°C) in an electrolyzer test station (CNL Energy). Preheated 1.0 M KOH was used as a reactant and 3 mL min -1 was injected (circulated) into the oxidation electrode at a flow rate of . No separate iR correction was performed. The test results are shown in Fig. 3g.

[0115]

[0116] Referring to FIGS. 3a to 3g, the catalyst (aRu# / Mo) according to the present inventionx C), the performance of platinum catalyst (Pt / C) and ruthenium catalyst (Ru / C) supported on a carbon support was evaluated for HER and HOR performance under strong alkaline conditions (1 M KOH). When comparing the performances obtained through linear scan voltammetry, the catalyst according to the present invention (aRu# / Mo x C) The ruthenium ensemble size is controlled according to the ruthenium content (Ru contents), and at this time, it can be confirmed that ideal performance is realized at a specific ensemble size, and at the same time, it can be confirmed that it exhibits kinetic performance that is more than 4 times superior to the existing carbon support-based noble metal particle catalysts (Pt / C and Ru / C). This shows that a specific ensemble size in the present invention can be an effective means to control the kinetic performance of the atomic-scale structure catalyst, and at the same time, it shows that the ruthenium ensemble (Ru ensemble)-molybdenum carbide interface system can significantly increase the kinetic performance for the hydrogen reaction under basic conditions compared to the carbon support.

[0117] In addition, referring to the stability evaluation results in the basic hydrogen evolution reaction (HER), it can be confirmed that the stability is significantly improved compared to carbon-supported noble metal particle catalysts (Pt / C and Ru / C), which can be evaluated as the effect of SMSI of the ruthenium ensemble and molybdenum carbide support due to high-temperature synthesis.

[0118]

[0119] As described above, the present invention is a catalyst in which ruthenium is supported in an ensemble form in an atomic-scale structure on the surface of a molybdenum carbide support dispersed on a carbon skeleton, and when applied to an electrochemical hydrogenation reaction under strong alkaline conditions, it can exhibit kinetic characteristics approximately four times superior to those of a commercial platinum catalyst.

[0120] In the case of noble metal ensemble catalysts, it is virtually impossible to stabilize several (up to 10) noble metal elements in a two-dimensional (2D) form on a support under specific synthetic conditions, and therefore, there is no strategy that can be commercially utilized. In the present invention, ruthenium acetylacetonate is selected as an ideal ruthenium precursor used in the synthesis, and by applying a self-assembly strategy, the ruthenium precursor interacts with phosphomolybdic acid to stabilize ruthenium (Ru) species in several forms at the precursor level. Subsequently, it was shown that the ruthenium species are selectively stabilized and arranged in an ensemble form on the surface of molybdenum carbide formed during a high-temperature heat treatment process. That is, we have presented a highly commercially viable technology that can easily implement a noble metal ensemble catalyst through simple heat treatment, and at the same time, control the ensemble size by controlling the amount of ruthenium precursor used in the synthesis.

[0121] In conventional technology, to increase the utilization of expensive precious metals, precious metal species were dispersed as single-atom catalysts and applied to electrochemical reactions. However, controlling the performance of the active sites of single-atom catalysts requires designing a support around the precious metal single atom or changing the precious metal species, which presents many limitations. In the present invention, by implementing a ruthenium ensemble (Ru ensemble), the performance of the active sites is controlled according to the ensemble size, and a new strategic approach of ensemble size control is proposed. This strategy maximizes the utilization of precious metals while simultaneously maximizing the kinetic performance per ruthenium.

[0122] Furthermore, in conventional technologies, low-temperature synthesis methods were primarily used to prevent sintering at high temperatures to stabilize the atomic-scale structure of precious metals. This prevents strong interactions between the support and the precious metal, resulting in low stability in electrochemical reactions. Many commercially available precious metal nanoparticle-based catalysts are supported on carbon-based supports, and carbon supports fail to form strong chemical bonds with the precious metal nanoparticle catalyst, limiting their stability to a certain extent. In this regard, the catalyst according to the present invention uses molybdenum carbide, which has a high affinity for noble metals, as a support, and simultaneously forms a strong chemical bond between the ruthenium ensemble (Ru ensemble) and molybdenum carbide through synthesis at high temperatures, thereby implementing SMSI, thereby selectively stabilizing the ruthenium ensemble (Ru ensemble) on the molybdenum carbide support, and through this, it was confirmed that not only does it maximize the utilization of noble metals, but also, due to the strong chemical bond, it exhibits stability that surpasses that of a commercial platinum catalyst in an electrochemical hydrogenation reaction.

[0123] Meanwhile, many commercial catalysts and previously developed single-atom catalysts are composed of carbon-based supports. In basic electrochemical hydrogenation, noble metal-based catalysts exhibit lower performance than those under acidic conditions due to the high activation energy for the water splitting reaction. To address this, strategies such as using noble metal alloy catalysts or decorating the surface of noble metal catalysts with metal oxides have been employed. However, these strategies have limitations due to the additional use of noble metals and the reduced exposure of the noble metal due to the decoration of the oxides. Furthermore, since these strategies cannot be applied to single-atom catalysts, it is rare to find examples of noble metal catalysts with atomic-scale structures being used for electrochemical hydrogenation under basic conditions. In the present invention, by utilizing molybdenum carbide, which has high water splitting performance, as a support for the ruthenium ensemble, the water splitting reaction is promoted near the ruthenium ensemble, demonstrating that kinetic performance is more than four times higher than that of noble metal catalysts utilizing carbon-based supports. That is, it was shown that the limitations of existing carbon-based supports can be overcome while significantly increasing the dynamic performance through the strategy of applying the multifunctional support according to the present invention to the base-condition electrochemical hydrogenation of the interface system.

[0124] On the other hand, most single-atom catalysts developed to date have rarely been applied to membrane electrode assemblies (MEAs) of anion-exchange membrane-based electrochemical conversion devices due to their low catalytic site density and poor kinetic performance. The catalyst of the present invention exhibits a high active site density and excellent kinetic performance and stability for electrochemical hydrogenation under basic conditions, demonstrating superior performance compared to commercial platinum catalysts when applied to actual membrane electrode assemblies (MEAs).

[0125]

[0126] The preferred embodiments of the present invention have been described in detail above. The description of the present invention is provided for illustrative purposes only, and those skilled in the art will readily appreciate that other specific modifications can be readily made without altering the technical spirit or essential features of the present invention.

[0127] Accordingly, the scope of the present invention is indicated by the claims described below rather than the detailed description above, and all changes or modifications derived from the meaning, scope and equivalent concepts of the claims should be interpreted as being included in the scope of the present invention.

Claims

1. A catalyst for electrochemical hydrogenation under basic conditions, wherein 2 to 20 ruthenium atoms are supported in an ensemble form on the surface of a molybdenum carbide-carbon nanocomposite support.

2. In paragraph 1, A catalyst for electrochemical hydrogenation under basic conditions, wherein the ensemble of the above rutheniums is a two-dimensional structure in which the ruthenium is exposed on the surface of the molybdenum carbide-carbon nanocomposite support.

3. In paragraph 1, A catalyst for electrochemical hydrogenation under basic conditions, characterized in that the ruthenium is contained in an amount of 1 to 15 wt% of the entire catalyst.

4. In paragraph 1, A catalyst for electrochemical hydrogenation under basic conditions, wherein the molybdenum carbide-carbon nanocomposite support has a porous structure.

5. In paragraph 1, A catalyst for an electrochemical hydrogen reaction, characterized in that the above electrochemical hydrogen reaction is a hydrogen production reaction or a hydrogen oxidation reaction.

6. An anion exchange membrane electrolysis or fuel cell catalyst electrode comprising a catalyst according to any one of claims 1 to 5.

7. A method for producing a catalyst according to claim 1, comprising the following steps: (A) a step of mixing a ruthenium precursor and a molybdenum precursor into a solution containing a carbon precursor; (B) a step of evaporating the solvent of the mixed solution to form a film; (C) a step of micronizing the film after the first heat treatment; and (D) A step of second heat treatment of the above undifferentiated catalyst.

8. In paragraph 7, A catalyst manufacturing method, characterized in that the ruthenium precursor is ruthenium acetylacetonate.

9. In paragraph 7, A method for producing a catalyst, characterized in that the carbon precursor is poly(ethylene oxide)-block-poly(styrene) (PEO-b-PS), phenol-formaldehyde resin (PF resin) or melamine-formaldehyde resin (MF resin), and the molybdenum precursor is phosphomolybdic acid.

10. In paragraph 7, A catalyst manufacturing method characterized in that the first heat treatment is performed at 80 to 200°C, and the second heat treatment includes the following steps: (D1) A step of introducing the above undifferentiated catalyst into a tubular sintering furnace, heat-treating it at 300 to 600°C for 1 to 10 hours and at 700 to 1,000°C for 2 to 15 hours in an argon gas flow, cooling it to room temperature, and maintaining it in a mixed gas flow of oxygen and argon for 5 to 30 hours to passivate it, and then undifferentiating it; (D2) a step of heat-treating the powder obtained in the step (D1) at 100 to 200°C for 2 to 15 hours in a mixed gas flow of oxygen and argon, and then cooling to room temperature to finely differentiate it; and (D3) A step of heat-treating the powder obtained in the step (D2) in an argon gas flow at a temperature of 700 to 2,000°C for 2 to 15 hours, cooling to room temperature, and maintaining it in a mixed gas flow of oxygen and argon for 5 to 30 hours to passivate it, and then finely disintegrating it.

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