Catalytic electrode for anion exchange membrane water electrolysis or fuel cell and method of making the same

Abstract

Disclosed is a catalyst for hydrogen evolution reaction or hydrogen oxidation reaction, which is a catalyst that can be used under alkaline conditions and has significantly improved kinetic characteristics compared to existing commercial platinum catalysts. The present invention provides a catalyst for electrochemical hydrogen reaction under alkaline conditions and a method for preparing the same, and a ruthenium-based catalytic electrode containing the same, which can be used as an electrode for anion exchange membrane-based water electrolysis cell and fuel cell, wherein the catalyst has 2 to 20 ruthenium supported in an aggregate form on the surface of a molybdenum carbide-carbon nanocomposite carrier.

Description

Technical Field

[0001] This invention relates to a catalytic electrode for water electrolysis or fuel cells and a method for preparing the same, and more specifically, to a catalytic electrode for anion exchange membrane water electrolysis or fuel cells and a method for preparing the same.

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2023-0171746, filed on November 30, 2023, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Water electrolysis technology is a technology that uses renewable energy-based electricity to produce hydrogen. This technology allows surplus electricity to be stored as hydrogen or the generated hydrogen to be used in processes such as oil refining and ammonia production, making it an environmentally friendly technology. In addition, fuel cell technology converts hydrogen into electricity, allowing the energy stored in hydrogen to be utilized locally. In both types of electrochemical conversion devices, the driving environment and characteristics depend on the type of electrolyte membrane used. Currently, cation exchange membrane-based conversion devices are closest to commercial application. However, in cation exchange membrane-based conversion devices, the electrode is driven under strongly acidic conditions, inevitably requiring the use of large amounts of precious metals in the oxygen electrode. Conversely, in anion exchange membrane-based conversion devices, the device is driven under strongly alkaline conditions. Under alkaline conditions, the kinetics of the electrochemical oxygen reaction are very fast, and non-precious metal catalysts can stably participate in the reaction, allowing the use of non-precious metal catalysts in the oxygen electrode. Therefore, the catalyst cost, which accounts for a significant portion of the conversion device's 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, for electrochemical hydrogen reactions under strongly alkaline conditions, the kinetic performance of commercial platinum catalysts is significantly reduced compared to strongly acidic conditions. This leads to a decrease in the efficiency of anion exchange membrane-based conversion devices, thus limiting their commercialization. Since the use of noble metals is unavoidable in electrochemical hydrogen reactions under strongly alkaline conditions, the commercialization of anion exchange membrane-based conversion devices can only be expected if noble metal-based catalysts are developed that exhibit high performance and high stability for hydrogen reactions under strongly alkaline conditions while reducing the amount of noble metals used.

[0005] Furthermore, to reduce catalyst costs, research on single-atom catalysts with structures that maximize the utilization of precious metals has been actively pursued in recent years. To synthesize single atoms, it is necessary to prevent sintering between metal atoms with atomic-scale structures; therefore, low-temperature synthesis methods with low metal loading are mainly employed. However, in the case of this catalyst, due to the limitations of the synthesis method, the active site density is low, and strong chemical bonds cannot be formed between the metal and the support at low temperatures, resulting in poor stability. Therefore, it cannot be used in membrane electrode assemblies (MEAs) for practical conversion devices. Summary of the Invention

[0006] This invention provides a catalyst for hydrogen evolution reaction or hydrogen oxidation reaction, a method for preparing the same, and a ruthenium-based catalytic electrode containing the catalyst, which can be used as an electrode for anion exchange membrane-based water electrolyzer and fuel cell. The catalyst is a catalyst that can be used under alkaline conditions and exhibits significantly improved kinetic characteristics compared to existing commercial platinum catalysts.

[0007] To address the aforementioned issues, the present invention provides a catalyst for electrochemical hydrogen reaction under alkaline conditions, wherein the catalyst has 2 to 20 ruthenium atoms supported in an aggregate form on the surface of a molybdenum carbide-carbon nanocomposite support.

[0008] Furthermore, the present invention provides a catalyst for electrochemical hydrogen reaction under alkaline conditions, characterized in that the aggregate formed by the interconnected ruthenium is a two-dimensional structure in which the ruthenium is exposed on the surface of the molybdenum carbide-carbon nanocomposite carrier.

[0009] Furthermore, the present invention provides a catalyst for electrochemical hydrogen reaction under alkaline conditions, characterized in that the ruthenium content in the catalyst is 1 to 15% by weight.

[0010] Furthermore, the present invention provides a catalyst for electrochemical hydrogen reaction under alkaline conditions, characterized in that the molybdenum carbide-carbon nanocomposite support has a porous structure.

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

[0012] Furthermore, the present invention provides a catalytic electrode comprising the above-described catalyst for anion exchange membrane water electrolysis or a fuel cell.

[0013] To address the aforementioned problem, this invention provides a method for preparing a catalyst, comprising the following steps:

[0014] Step (A): Mix the ruthenium precursor and the molybdenum precursor with a solution containing a carbon precursor;

[0015] Step (B) involves evaporating the solvent in the mixed solution to generate a thin film;

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

[0017] Step (D) involves subjecting the micronized catalyst to a second heat treatment.

[0018] Furthermore, the present invention provides a method for preparing a catalyst, wherein the ruthenium precursor is ruthenium acetylacetone.

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

[0020] Furthermore, the present invention provides a catalyst preparation method, characterized in that the first heat treatment is performed at 80–200°C, and the second heat treatment includes the following steps:

[0021] Step (D1): The micronized catalyst is fed into a tubular calcination furnace and heat-treated in an argon gas flow at 300-600°C for 1-10 hours and at 700-1,000°C for 2-15 hours. Then it is cooled to room temperature and passivated in a mixed gas flow of oxygen and argon for 5-30 hours before being micronized.

[0022] Step (D2): The micropowder obtained in step (D1) is heat-treated in a mixed gas flow of oxygen and argon at 100–200°C for 2–15 hours, then cooled to room temperature and micronized; and

[0023] Step (D3) involves heat-treating the micropowder obtained in step (D2) at 700–2,000°C for 2–15 hours in an argon gas flow, then cooling it to room temperature, and passivating it by holding it in a mixed gas flow of oxygen and argon for 5–30 hours before micronization.

[0024] This invention relates to a catalyst in which ruthenium is loaded in an atomic-scale aggregate form on the surface of a molybdenum carbide-carbon nanocomposite support with molybdenum carbide embedded in a carbon skeleton. When this catalyst is applied to the electrochemical hydrogen reaction under strongly alkaline conditions, it can achieve kinetic properties that are about 4 times better than those of commercial platinum catalysts. Attached Figure Description

[0025] Figures 1a to 1g The images show the results of scanning transmission electron microscopy (STEM), energy-dispersive X-ray mapping (EDX), and scanning electron microscopy (SEM) analysis of the catalyst prepared in Example 2.

[0026] Figures 2a to 2d The graphs represent the X-ray absorption near edge structure (XANES) and Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) analysis results of the catalyst prepared in Experimental Example 3.

[0027] Figures 3a to 3g The graphs represent the results of tests conducted on the catalyst prepared in Example 4 under strongly alkaline conditions for hydrogen evolution reaction (HER) performance and stability, hydrogen oxidation reaction (HOR) performance, and application in a membrane-electrode assembly (MEA). Detailed Implementation

[0028] The present invention will now be described in detail through preferred embodiments. Prior to this, the terms or words used in this specification and claims should not be limited to their conventional or dictionary meanings, but should be interpreted as conforming to the meaning and concept of the technical idea of ​​the present invention, based on the principle that the inventors may appropriately define the concepts of terms in order to best illustrate their invention. Therefore, the structures of the embodiments described in this specification are merely one of the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. It should be understood that various equivalents and modifications may exist to replace these embodiments at the time of filing this application.

[0029] This invention discloses a catalyst for electrochemical hydrogen reaction under alkaline conditions, wherein the catalyst is loaded with 2 to 20 ruthenium atoms in an aggregate form on the surface of a molybdenum carbide-carbon nanocomposite support.

[0030] In this invention, the ruthenium loaded in an aggregate form is loaded in an atomic-scale structure consisting of 2 to 20 ruthenium atoms connected together on the surface of a molybdenum carbide-carbon nanocomposite carrier in which molybdenum carbide is embedded in a carbon skeleton.

[0031] The catalyst of the present invention is a catalyst for hydrogen evolution reaction or hydrogen oxidation reaction under alkaline conditions. It is composed of a ruthenium aggregate-porous molybdenum carbide / carbon nanocomposite material prepared by utilizing the molecular interaction between metal precursors. It is used as an electrode catalyst for water electrolyzers and fuel cells based on anion exchange membranes.

[0032] In this invention, the ruthenium is derived from a specific precursor. Specifically, by selecting ruthenium acetylacetonate as the ruthenium precursor for synthesis, the molecular interactions between metal precursors can be utilized to synthesize ruthenium aggregate catalysts with different loadings of ruthenium onto porous molybdenum carbide / carbon nanocomposite materials.

[0033] Here, when using existing ruthenium precursors such as ruthenium chloride, the interaction between ruthenium precursors is too strong, and a large number of ruthenium agglomerates are formed due to the lack of interaction between the ruthenium precursor and the molybdenum precursor. As a result, the utilization rate of ruthenium will be greatly reduced, and there is a problem of a significant decrease in the electrochemical performance per unit of precious metal.

[0034] In contrast, when ruthenium acetylacetonate is used as a ruthenium precursor according to the present invention, the ruthenium chemical species can be uniformly dispersed in the support without large-sized ruthenium aggregates through its interaction with phosphomolybdic acid, which is a molybdenum precursor. Thus, even under high loading conditions, ruthenium ensemble catalysts with atomic-scale structures can be easily synthesized.

[0035] At this time, the ruthenium aggregate consists of 2 to 20, preferably 2 to 10, ruthenium atoms interconnected in an atomic-scale structure. In this invention, the ruthenium aggregate can be selectively loaded onto the molybdenum carbide and form a two-dimensional structure exposed on the surface of the molybdenum carbide-carbon nanocomposite carrier.

[0036] The selective loading and two-dimensional structure formation of such ruthenium aggregates are achieved by selecting specific molybdenum compounds as supports and employing a high-temperature synthesis method instead of the existing low-temperature synthesis method. Specifically, this invention uses a molybdenum carbide-carbon nanocomposite material with molybdenum carbide embedded in a porous carbon framework (mesoporous structure) as a support, and employs a high-temperature synthesis method. This achieves a strong interaction between the ruthenium catalyst and the molybdenum support, allowing the ruthenium aggregates to be selectively loaded onto the molybdenum carbide. Through this strong metal-support interaction (SMSI), the utilization rate of ruthenium is maximized while significantly improving the stability in the electrochemical catalytic reaction.

[0037] The molybdenum carbide exhibits a high affinity for noble metal chemical species, enabling ruthenium chemical species to maintain a stable atomic-scale structure under high-temperature synthesis conditions. This results in ruthenium chemical species having a two-dimensional (2D) aggregate morphology rather than a three-dimensional (3D) cluster morphology, thereby maximizing ruthenium utilization and optimizing electrochemical hydrogen reaction performance.

[0038] In the case of existing particulate catalysts with three-dimensional structures, only the elements exposed on the surface are used as active sites. However, in the case of the aggregate catalyst synthesized according to the present invention, which has a two-dimensional structure, all ruthenium chemical species are exposed on the surface. Therefore, all ruthenium elements can be utilized, thereby maximizing the utilization rate of the precious metal and significantly reducing the amount of precious metal used. Specifically, the present invention uses ruthenium (Ru), which costs only about one-third of platinum (Pt), to replace platinum (Pt) commonly used in hydrogen reactions. This is also very advantageous in terms of commercialization. In particular, the strong metal-support interaction (SMSI) achieved by the high-temperature synthesis method enables molybdenum carbide to exert a very strong stabilizing effect on the ruthenium aggregate (Ru ensemble), resulting in significantly improved electrochemical stability compared to existing catalysts.

[0039] Thus, this invention achieves a ruthenium aggregate-molybdenum carbide interface system through the strong interaction between the ruthenium aggregate and molybdenum carbide, and applies this interface system to the electrochemical hydrogen reaction under strongly alkaline conditions. This results in a significant improvement in kinetic performance of more than 4 times compared with existing platinum-based or ruthenium-based catalysts, thereby reducing catalyst costs while improving kinetic performance and greatly enhancing the commercial viability of anion exchange membrane-based conversion devices.

[0040] Specifically, in the electrochemical hydrogen reaction under strongly alkaline conditions, the kinetic performance of commercial platinum catalysts is significantly reduced compared to that under strongly acidic conditions due to the high activation energy of the hydrolysis reaction. In contrast, the molybdenum carbide support significantly improves the kinetic characteristics of the electrochemical hydrogen reaction occurring at the surrounding ruthenium active sites by substantially reducing the activation energy of the hydrolysis reaction. Furthermore, the catalyst of this invention does not disperse ruthenium in single-atom form, but rather in an ensemble of two or more ruthenium chemical species interconnected, thereby overcoming the limitations of existing single-atom catalysts.

[0041] At this point, the size or amount of the ruthenium aggregate will change the adsorption energy of the reactants. Therefore, the present invention predicts that there exists an ideal aggregate size or amount that can significantly improve the performance of a unit precious metal. Experiments have confirmed that when the content of ruthenium in the catalyst is 1 to 15% by weight, preferably 2 to 10% by weight, and more preferably 3 to 8% by weight, the most ideal performance improvement can be achieved.

[0042] As described above, when the catalyst of the present invention is applied to anion exchange membrane-based conversion devices, it achieves performance that surpasses that of existing commercial platinum catalysts. The ruthenium aggregate catalyst prepared by high-temperature synthesis exhibits significantly improved active site density, kinetic performance and stability, demonstrating performance far exceeding that of commercial platinum catalysts in actual membrane electrode assembly (MEA) applications. This is a performance that existing single-atom catalysts have not shown.

[0043] The preparation method of the catalyst for hydrogen evolution reaction or hydrogen oxidation reaction under alkaline conditions, as described in this invention, will be described in detail below.

[0044] The method for preparing a catalyst for hydrogen evolution reaction or hydrogen oxidation reaction under alkaline conditions according to the present invention includes the following steps: step (A), mixing a ruthenium precursor and a molybdenum precursor with a solution containing a carbon precursor; step (B), evaporating the solvent in the mixed solution to generate a thin film; step (C), micronizing the thin film after a first heat treatment; and step (D), performing a second heat treatment on the micronized catalyst.

[0045] In this invention, a series of improved interaction mediator-assisted evaporation-induced self-assembly (IM-EISA) methods were used to synthesize catalysts, which involved (A) precursor mixing, (B) thin film formation, (C) micronization after a first heat treatment, and (D) a second heat treatment. This demonstrated that catalysts with significantly improved kinetic properties for hydrogen evolution reactions or hydrogen oxidation reactions could be prepared.

[0046] As mentioned above, ruthenium acetylacetonate is preferred as a ruthenium precursor, and phosphomolybdic acid is preferred as a molybdenum precursor.

[0047] In step (A), a precursor solution is prepared by mixing the ruthenium precursor and the molybdenum precursor with a solution containing a carbon precursor. The carbon precursor can be a block copolymer or an organic polymer. The block copolymer is not particularly limited, as long as it is a substance that introduces the synthesized molybdenum carbide into the porous structure of the carbon skeleton through self-assembly, while uniformly dispersing the metal chemical species on the carbon skeleton. For example, it can be poly(ethylene oxide)-block-poly(styrene), PEO-b-PS. When PEO-b-PS is mixed with the molybdenum precursor in a specific ratio, the molybdenum precursor and the PEO block interact strongly and are selectively located. Furthermore, the organic polymer is not particularly limited, as long as it can form a carbon skeleton and be used as a carbon source for the molybdenum carbide precursor. For example, it can be phenolic resin (PF resin) or melamine-formaldehyde resin (MF resin). When subjected to subsequent heat treatment, it forms a stable nanostructure through cross-linking.

[0048] Specifically, in the case of the organic polymer, the porous structure formed through crosslinking during the first heat treatment is stabilized and simultaneously serves as the carbon source for both the carbon skeleton and the molybdenum carbide process. Furthermore, during the second heat treatment, the crosslinked organic polymer transforms into a carbon skeleton, while the molybdenum precursor decomposes and reacts with the carbon skeleton to form molybdenum carbide. Due to the presence of the carbon skeleton, the molybdenum carbide nanoparticles are stabilized and do not overgrow. In the case of the MF resin, it acts as an interaction mediator and carbon source, enhancing the interaction between the molybdenum precursor and the block copolymer, thereby enabling the formation of molybdenum carbide in the form of small-sized nanoparticles.

[0049] At this point, by sonicating and stirring the precursor solution, the precursor can be completely dissolved in solvents such as tetrahydrofuran (THF) for self-assembly.

[0050] In step (B), the solvent in the mixed solution of step (A) is evaporated to generate a thin film; in step (C), the generated thin film is subjected to a first heat treatment followed by micronization. The first heat treatment can be performed at 80–200°C, preferably at 90–150°C for 12–84 hours, and more preferably at 90–120°C for 24–72 hours.

[0051] Step (D) is a process of obtaining the final catalyst by subjecting the micro powder obtained after the first heat treatment to three consecutive heat treatments.

[0052] Specifically, step (D) may include: step (D1), feeding the micronized catalyst into a tube calcination furnace (tube furnace). In a furnace, the powder is heat-treated at 300–600°C for 1–10 hours and at 700–1,000°C for 2–15 hours in an argon gas flow, then cooled to room temperature and kept in a mixed oxygen and argon gas flow for 5–30 hours for passivation before being micronized (first heat treatment); in step (D2), the micronized powder obtained in step (D1) is heat-treated at 100–200°C for 2–15 hours in a mixed oxygen and argon gas flow, then cooled to room temperature and micronized (second heat treatment); and in step (D3), the micronized powder obtained in step (D2) is heat-treated at 700–2,000°C for 2–15 hours in an argon gas flow, then cooled to room temperature and kept in a mixed oxygen and argon gas flow for 5–30 hours for passivation before being micronized (third heat treatment).

[0053] In the first heat treatment, the initial argon (Ar) flow rate can be 50–500 sccm, preferably 100–300 sccm. Furthermore, during continuous heat treatment, it is preferable to perform heat treatment at 400–500°C for 2–5 hours and at 800–900°C for 4–8 hours. Afterward, upon cooling to room temperature, the flow rates of the oxygen (O2) and argon (Ar) mixture can be 0.1–10 sccm and 50–500 sccm, preferably 0.5–5 sccm and 100–300 sccm, respectively, and the treatment time is preferably 5–30 hours.

[0054] Furthermore, in the second heat treatment, the flow rates of the mixed gas of oxygen (O2) and argon (Ar) can be 5-50 sccm and 10-200 sccm, respectively, preferably 10-30 sccm and 50-100 sccm, and preferably the heat treatment is carried out at 110-150°C for 3-10 hours.

[0055] In the third heat treatment, the initial argon (Ar) flow rate can be 50–500 sccm, preferably 100–300 sccm. Furthermore, it is preferable to perform the heat treatment at 800–1500°C for 3–10 hours. Afterward, upon cooling to room temperature, the flow rates of the oxygen (O2) and argon (Ar) mixture can be 0.1–10 sccm and 50–500 sccm, preferably 0.5–5 sccm and 100–300 sccm, respectively, and the treatment time can preferably be 5–30 hours.

[0056] The following describes specific embodiments of the present invention.

[0057] Examples and Comparative Examples

[0058] (1) Preparation of ruthenium precursor solution

[0059] Ruthenium(III) acetylacetone (Ru(acac)3) was dissolved in tetrahydrofuran (THF) solution and used as follows, depending on the proportion of ruthenium to be prepared:

[0060] - aRu1 / Mo x C: 5mL THF + 21.8mg Ru(acac)3

[0061] - aRu2 / Mo x C: 5mL THF + 43.7mg Ru(acac)3

[0062] - aRu3 / Mo x C: 5mL THF + 65.5mg Ru(acac)3

[0063] - aRu4 / Mo x C: 5mL THF + 87.3mg Ru(acac)3

[0064] - aRu5 / Mo x C: 5mL THF + 131.0mg Ru(acac)3

[0065] (aRu# / Mo x In C, "a" indicates "atomically dispersed" or "atom-dimension structured".

[0066] In addition, in order to prepare the comparative example Ru / Mo x C_Cl, using ruthenium(III) chloride hydrate as follows:

[0067] -Ru / Mo xC_Cl: 5mL THF + 74.1mg RuCl3·xH2O

[0068] (2) Preparation of catalyst

[0069] The catalyst was synthesized using an improved interaction mediator-assisted evaporation-induced self-assembly (IM-EISA) method.

[0070] First, 0.1 g of phenolic resin (PF resin), 0.02 g of melamine-formaldehyde resin (MF resin), and 0.2 g of PEO-b-PS (Mn=50 kg / mol, PEO content 10.0 wt%, polydispersity = 1.25) were dissolved in 25 mL of tetrahydrofuran (THF). The mixture was then stirred at room temperature for 2 hours to form a transparent solution. Next, a ruthenium precursor solution was added to the mixture and stirred for 10 minutes. Then, 0.2 g of phosphomolybdic acid (PMA) was added to the mixture, and after ultrasonic treatment for 30 minutes, it was stirred for 30 minutes to ensure complete dissolution. Subsequently, the mixture was placed at 50°C for 12 hours to allow the solvent to slowly evaporate. The resulting film was then further heat-treated at 100°C for 48 hours. Afterward, the film was pulverized for 10 minutes to achieve micronization. Finally, the catalyst was obtained through a three-stage heat treatment process.

[0071] (i) First heat treatment: The micronized powder was added to a tube furnace, and argon gas (Ar, 200 sccm) was introduced. The furnace was held at 450°C for 3 hours (heating rate: 1°C / min), followed by heat treatment at 850°C for 6 hours (heating rate: 5°C / min), and then cooled to room temperature (cooling rate: 5°C / min). The sample at room temperature was then passivated for 24 hours in a mixed gas flow of oxygen (O2, 2 sccm) / argon (Ar, 200 sccm). The resulting powder was then further pulverized for 10 minutes for micronization.

[0072] (ii) Second heat treatment: The powder obtained after the first heat treatment is placed in a tube furnace and treated at 130°C for 6 hours in a mixed gas flow of oxygen (O2, 20 sccm) / argon (Ar, 80 sccm) (=20 vol% O2 / Ar) (heating rate: 2°C / min), and then cooled to room temperature (cooling rate: 2°C / min). After that, it is pulverized for 10 minutes to achieve micronization.

[0073] (iii) Third (final) heat treatment: The powder obtained after the second heat treatment was placed in a tube furnace and heat-treated at 1,100°C for 6 hours in an argon (Ar, 200 sccm) gas flow (heating rate: 5°C / min), and then cooled to room temperature (cooling rate: 5°C / min). Afterwards, the sample at room temperature was passivated in an oxygen (O2, 2 sccm) / argon (Ar, 200 sccm) mixed gas flow for 24 hours. Micronization was then performed by pulverizing for 10 minutes.

[0074] The catalyst aRu# / Mo is ultimately obtained through the above process. x C. Herein, the catalyst of the present invention obtained using ruthenium acetylacetonate is designated as aRu# / Mo. x C, while the catalyst of the comparative example obtained using ruthenium chloride is labeled Ru / Mo. x C_Cl. The higher the ruthenium content, the larger the value of the # symbol.

[0075] Experimental Example 1

[0076] The ruthenium content in the catalyst prepared above was determined by the following method, and the results are shown in Table 1 below.

[0077] [Determination Method]

[0078] The catalyst was dissolved in aqua regia using a microwave reaction and then measured using an Agilent ICP-MS 7700S instrument. The average of five measurements was taken.

[0079] [Table 1]

[0080]

[0081] Experimental Example 2

[0082] The catalysts prepared above were analyzed using scanning transmission electron microscopy (STEM), energy-dispersive X-ray EDX mapping, and scanning electron microscopy (SEM) according to the following methods. The results are presented below. Figures 1a to 1g .

[0083] [STEM, EDX energy dispersive spectroscopy and SEM analysis methods]

[0084] For STEM and EDX energy dispersive spectroscopy, measurements were performed using a Tecnai G2 F30 S-Twin (FEI) instrument at an accelerating voltage of 300 kV. For SEM, measurements were performed using a Hitachi SU8230 instrument.

[0085] Reference Figures 1a to 1g It can be confirmed that the catalysts synthesized via the self-assembly strategy all possess porous structures and exhibit a morphology of molybdenum carbide nanoparticles uniformly dispersed (embedded) within a carbon framework. Furthermore, STEM-EDX energy dispersive spectroscopy analysis confirms that the aRu# / Mo catalyst obtained using ruthenium acetylacetonate... x In the case of C catalyst, ruthenium agglomerates are absent; instead, they are selectively and uniformly dispersed on the molybdenum carbide support, exhibiting an atomic-scale structure. Conversely, the Ru / Mo mixture obtained using ruthenium chloride... x In the case of a C-Cl catalyst, very large (approximately 100 nm) ruthenium agglomerates are formed, and it is predicted that the utilization rate of the noble metal in this catalyst will be significantly reduced. That is, according to the present invention, by applying ruthenium acetylacetonate to the self-assembly process, it can interact with phosphomolybdic acid, which is a molybdenum precursor, thereby stabilizing at a level of several (less than 10) agglomerates in the precursor stage. After a high-temperature synthesis process, such as... Figures 1a to 1g As shown, selective stabilization at the atomic-scale structural level is achieved on molybdenum carbide supports. However, in the case of ruthenium chloride, stabilization cannot be achieved through intermolecular interactions, therefore... Figures 1a to 1g As shown, large agglomerates were formed.

[0086] Experimental Example 3

[0087] The catalysts prepared above were analyzed using X-ray absorption near-edge structure (XANES) and Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) methods as described below, and the results are presented in the table below. Figures 2a to 2d For comparison, results for ruthenium dioxide (RuO2) and ruthenium foil are also shown.

[0088] [XANES and FT-EXAFS Analysis Methods]

[0089] To obtain X-ray absorption spectroscopy (XAS) data such as XANES and FT-EXAFS, ruthenium K-edge analysis was performed using the 8C nano-XAFS beamline at the Pohang Accelerator Laboratory (PAL).

[0090] Reference Figures 2a to 2d In the catalyst of the present invention (aRu2 / Mo) x In case C), strong chemical bonds are formed between the catalyst and the molybdenum carbide support through a high-temperature synthesis process, achieving strong metal-support interaction (SMSI). The molybdenum carbide support is a support with metallic characteristics, while most single-atom catalysts are stabilized by elements or ligands such as oxygen (O), nitrogen (N), and sulfur (S), or are stabilized on supports with non-metallic characteristics such as oxides, and therefore usually have high oxidation numbers. In contrast, the catalyst of this invention (aRu# / Mo) x In case C), due to the strong interaction between the ruthenium ensemble catalyst and the molybdenum carbide as a metallic support, its oxidation number is close to that of the ruthenium foil, unlike existing single-atom catalysts. This demonstrates that strong metal-support interaction (SMSI) can be achieved through the strategy of the present invention.

[0091] Furthermore, referring to the Fourier transform extended X-ray absorption fine structure (FT-EXAFS) results, it can be confirmed that the catalyst of the present invention (aRu# / Mo) xC) Stabilization to an atomic-scale structure via Ru-C chemical bonds; as the value of # increases, the peak height corresponding to the Ru-Ru chemical bond increases, thus confirming that the aggregate size of sub-nanometer ruthenium clusters can be adjusted by regulating the amount of ruthenium precursor. Furthermore, this is related to ruthenium foil and Ru / Mo... x Compared to C-Cl, the Ru-Ru shell peak is very low, which confirms that it forms Ru-Ru chemical bonds corresponding to a two-dimensional ensemble structure.

[0092] Test Example 4

[0093] For the catalyst prepared above, performance and stability tests were conducted under strongly alkaline conditions for hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), and application in membrane electrode assembly (MEA) according to the following methods. The results are presented below. Figures 3a to 3g For comparison, results for existing commercial platinum catalysts (Pt / C) and ruthenium catalysts (Ru / C) are also presented. The commercial platinum catalyst (Pt / C) used was HISPEC 3,000 (Johnson Matthey Co.); the Ru / C catalyst used was prepared by the following chemical reduction method: 167.3 mg of RuCl3·xH2O was dissolved in 60 mL of anhydrous ethanol (sonicated for 10 minutes and stirred for 1 hour), then 0.3 g of commercial carbon (Vulcan XC-72R) was added and dispersed (sonicated for 10 minutes) and stirred. Then, a solution of 0.6 g of NaBH4 dissolved in 50 mL of anhydrous ethanol was dropwise added to the above mixture and slowly mixed. The catalyst was obtained by vacuum filtration.

[0094] [HER, stability, HOR, and MEA testing methods]

[0095] Electrochemical Characterization

[0096] The electrochemical half-cell was measured using a potentiostat (Reference 600, Gamry Instruments) in a three-electrode system. The reference electrode was a Hg / HgO electrode immersed in 1M NaOH solution. A graphite rod was used as the counter electrode. Additionally, a 5mm diameter glassy carbon-rotating disk electrode (RDE) was used as the substrate for the catalyst ink. Before coating with the catalyst ink, the RDE was polished sequentially with 0.3μm and 0.05μm polishing slurries (alumina polishing slurry). Before preparing the catalyst ink, 40mg of Vulcan XC 72R was dispersed in 20mL of isopropanol (IPA / C) by sonication for 20 minutes. To prepare the catalyst ink, 15.3mg, 8.8mg, 5.4mg, 4.1mg, and 3.0mg of aRuX / Mo were used. x C (corresponding to X=1, 2, 3, 4, 5 respectively) were dispersed by ultrasonic treatment for more than 1 hour in 400 μL of distilled water and 1600 μL of IPA / C solutions diluted with 76 μL, 44 μL, 27 μL, 20 μL, and 15 μL of Sustainion® XA-9 alkaline ionomer, respectively. Pt / C catalyst ink was prepared using 2.2 mg of Pt / C catalyst, 389 μL of distilled water, 11 μL of Sustainion® XA-9 alkaline ionomer, and 1600 μL of IPA / C solvent. Ru / C catalyst ink was prepared using 2.8 mg of catalyst, 386 μL of distilled water, 14 μL of Sustainion® XA-9 alkaline ionomer, and 1600 μL of IPA / C solvent.

[0097] Next, 12 μL of catalyst ink was dropped onto a rotating disk electrode (RDE), and the electrode was dried by rotating at 400 rpm. To produce a uniform electrode, the loading process was repeated three times, resulting in a ruthenium loading of 0.040 mg / cm³. 2 (The Pt loading in Pt / C is 0.042 mg / cm³) 2Electrodes were prepared for the target. Before conducting the electrochemical experiments, the polytetrafluoroethylene (PTFE) electrolytic cell and bubbler were soaked at 60°C for more than 1 hour to remove impurities. Subsequently, measurements were taken in a 1.0 MkOH solution saturated with H2, and the voltage was calibrated and expressed as a potential relative to the reversible hydrogen electrode (RHE).

[0098] In addition, prior to the measurements, an activation process was performed to electrochemically clean the electrode surface using cyclic voltammetry (CV) at 1600 rpm with a scan rate of 100 mV / s within the range of −600 to 600 mV, consisting of 40 cyclic scans. Polarization curves were measured using linear sweep voltammetry (LSV) at 1600 rpm with a scan rate of 1 mV / s, and iR correction was applied to eliminate the influence of capacitive current. The HER polarization curve was measured within the range of 20 mV to −300 mV, and the HOR polarization curve within the range of −20 mV to 150 mV. The HER Tafel plot is represented by the following mathematical formula 1. HER durability (stability) testing was conducted at 1600 rpm and −20 mA / cm². 2 Under certain conditions, chronopotentiometry (CP) was used for 24 hours.

[0099] <Mathematical Formula 1>

[0100]

[0101] In mathematical formula 1, η is the overpotential and j is the current density.

[0102] exist Figures 3a to 3g In the figure, the HER polarization curve and the HOR polarization curve are shown respectively. Figure 3a and Figure 3b The mass activity assay results are shown in Figure 3c and Figure 3d The results of the Hertzsprung-Tafel plot are shown in... Figure 3e The HER durability (stability) test results are shown in Figure 3f.

[0103] <Determination of Anion Exchange Membrane Water Electrolyzer (AEMWE)>

[0104] The membrane electrode assembly (MEA) is fabricated by placing a PiperION® anion exchange membrane (20 μm thick, self-supporting membrane) between the anode (oxidation electrode) and the cathode (reduction electrode). The geometric active area of ​​the MEA is 1 cm². 2 The prepared aRu2 / Mo x C catalyst was used as the cathode catalyst, and 0.2 mg Ru / cm² was coated onto the carbon fiber electrode (Sigracet 39BB) using a spray coating method. 2 Preparation was carried out. Furthermore, NiFe catalyst was used as the anode catalyst, and a 3.0 mg / cm³ coating was applied to a stainless steel fiber electrode (SS Fiber Paper) using a spraying method. 2 Preparation was carried out. aRu2 / Mo x C catalyst ink uses aRu2 / Mo x The catalyst was prepared using 50 mg of C catalyst, 0.75 mL of distilled water, 0.75 mL of absolute ethanol, 1.5 mL of isopropanol (IPA), and 98.2 mL of 5 wt% PiperION® anion exchange dispersion. The NiFe catalyst ink was prepared using 60 mg of catalyst, 0.9 mL of distilled water, 0.9 mL of absolute ethanol, 1.8 mL of isopropanol (IPA), and 161.4 mL of 5 wt% PiperION® anion exchange dispersion. Both were dispersed by sonication for at least 3 hours. Electrodes were then fabricated using a spray coating method. Both the electrodes and the membrane were then soaked in 1.0 M KOH solution for at least 24 hours to pre-activate the anion dispersion and the anion exchange membrane. After washing with distilled water, an electrolytic cell was fabricated.

[0105] Single-cell tests were conducted in an electrolyzer teststation (CNL Energy). Temperatures were adjusted (60–90 °C), and voltages were maintained for 2 minutes at 0.05 V intervals within a range of 1.35–2.10 V. Measurements were performed using a potentiostatic method. Preheated 1.0 M KOH was used as the reactant and circulated into the oxidation electrode at a flow rate of 3 mL / min. No additional iR correction was performed throughout the process. The test results are presented below. Figure 3g .

[0106] Reference Figures 3a to 3g Under strongly alkaline conditions (1M KOH), the catalyst of the present invention (aRu# / Mo) x C) The performance of platinum catalyst (Pt / C) and ruthenium catalyst (Ru / C) supported on carbon supports was evaluated using HER and HOR methods. The results confirmed that, when comparing the performance obtained by linear scan voltammetry, the catalyst of the present invention (aRu / C) performed better. x In C), the ruthenium ensemble size is adjusted by the ruthenium content, achieving ideal performance at a specific ensemble size and exhibiting kinetic performance more than four times better than existing carbon-supported noble metal particle catalysts (Pt / C and Ru / C). This indicates that, in this invention, a specific ensemble size can serve as an effective means of regulating the kinetic performance of atomically structured catalysts, and also demonstrates that the ruthenium ensemble-molybdenum carbide interface system can significantly improve the hydrogen reaction kinetics under alkaline conditions compared to carbon supports.

[0107] Furthermore, the stability evaluation results of the hydrogen evolution reaction (HER) under alkaline conditions confirm that the catalyst of the present invention has significantly improved stability compared with carbon-supported noble metal particulate catalysts (Pt / C and Ru / C). This can be attributed to the effect of strong metal-support interaction (SMSI) between the ruthenium ensemble formed by high-temperature synthesis and the molybdenum carbide support.

[0108] In summary, the present invention relates to a catalyst in which ruthenium is supported in an atomic-scale aggregate form on the surface of a molybdenum carbide support dispersed on a carbon skeleton. When this catalyst is applied to an electrochemical hydrogen reaction under strongly alkaline conditions, it can achieve kinetic properties that are about 4 times better than those of commercial platinum catalysts.

[0109] In the case of noble metal ensemble catalysts, it is nearly impossible to stabilize several (up to 10) noble metal elements in a two-dimensional (2D) form on a support under specific synthetic conditions, thus there is currently no commercially applicable strategy. In this invention, ruthenium acetylacetonate is selected as the ideal ruthenium precursor for synthesis, and a self-assembly strategy is applied. Through the interaction between the ruthenium precursor and phosphomolybdic acid, the ruthenium (Ru) chemical species are stabilized into several forms in the precursor stage. Subsequently, molybdenum carbide is formed during high-temperature heat treatment, and the ruthenium chemical species are selectively stabilized on the surface of molybdenum carbide and arranged in an aggregate form. That is, this invention proposes a commercially viable technique that can easily realize noble metal ensemble catalysts through simple heat treatment, and the ensemble size can be adjusted by regulating the amount of ruthenium precursor.

[0110] In existing technologies, to improve the utilization rate of expensive precious metals, precious metal chemical species are dispersed into single-atom catalysts and applied to electrochemical reactions. However, to adjust the performance of the active sites of single-atom catalysts, the support surrounding the precious metal single atoms needs to be designed or the precious metal chemical species replaced, thus presenting many limitations. In this invention, a novel strategic method for adjusting the ensemble size is proposed, whereby the performance of the active sites is adjusted according to the ensemble size by realizing a ruthenium ensemble. Through the strategy of this invention, the utilization rate of precious metals can be maximized, while the kinetic performance per unit of ruthenium can also be maximized.

[0111] Furthermore, in existing technologies, low-temperature synthesis methods are primarily used to stabilize noble metals at the atomic scale to prevent sintering at high temperatures. Consequently, strong interactions are not formed between the support and the noble metal, resulting in lower stability in electrochemical reactions. In the case of noble metal nanoparticle-based catalysts, most commercial catalysts are supported on carbon supports, but carbon supports cannot form strong chemical bonds with noble metal nanoparticle catalysts, thus limiting their stability. In contrast, the catalyst of this invention uses molybdenum carbide, which has a high affinity for noble metals, as a support. Simultaneously, strong chemical bonds are formed between ruthenium ensembles and molybdenum carbide through high-temperature synthesis, achieving strong metal-support interaction (SMSI). This allows the ruthenium ensembles to be selectively stabilized on the surface of the molybdenum carbide support, thereby maximizing the utilization of the noble metal and exhibiting stability exceeding that of commercial platinum catalysts in electrochemical hydrogen reactions due to the strong chemical bonds.

[0112] Furthermore, most commercial catalysts and previously developed single-atom catalysts are composed of carbon supports. In the case of electrochemical hydrogen reactions under alkaline conditions, the performance of noble metal-based catalysts is lower than under acidic conditions due to the high activation energy of the hydrolysis reaction. To address this issue, strategies have been employed such as using noble metal alloy catalysts or modifying the surface of noble metal catalysts with metal oxides. However, this strategy is limited by the reduced exposure of noble metals due to the additional use of noble metals and oxides. Moreover, this strategy cannot be applied to single-atom catalysts, making it difficult to find examples of applying noble metal catalysts with atomic-scale structures to electrochemical hydrogen reactions under alkaline conditions. In this invention, by using molybdenum carbide, which has high hydrolysis performance, as a support for ruthenium ensembles, the hydrolysis reaction near the ruthenium ensemble is promoted, thereby exhibiting kinetic performance more than four times higher than that achieved by noble metal catalysts using carbon supports. In other words, the strategy of applying a multifunctional support interface system to electrochemical hydrogen reactions under alkaline conditions, as described in this invention, demonstrates the ability to overcome the limitations of existing carbon supports while significantly improving kinetic performance.

[0113] On the other hand, most single-atom catalysts developed to date have rarely been used in membrane electrode assemblies (MEAs) of anion exchange membrane-based electrochemical conversion devices due to their low active site density and poor kinetic performance. With the catalyst of this invention, it has been confirmed that due to its high active site density, excellent electrochemical hydrogen reaction kinetics under alkaline conditions, and stability, it can achieve superior performance compared to commercial platinum catalysts when practically applied to MEAs.

[0114] The preferred embodiments of the present invention have been described in detail above. The description of the present invention is for illustrative purposes only, and those skilled in the art should understand that the present invention can be readily modified into other specific forms without altering its technical concept or essential features.

[0115] Therefore, the scope of the invention should be defined by the claims rather than the foregoing detailed description, and all modifications or variations derived from the meaning, scope and equivalent concepts of the claims should be interpreted as being included within the scope of the invention.

Claims

1. A catalyst for an electrochemical hydrogen reaction under alkaline conditions, wherein, The catalyst is loaded with 2 to 20 ruthenium atoms in an aggregate form on the surface of a molybdenum carbide-carbon nanocomposite support.

2. The catalyst for electrochemical hydrogen reaction under alkaline conditions according to claim 1, characterized in that, The aggregate formed by the interconnected ruthenium is a two-dimensional structure in which the ruthenium is exposed on the surface of the molybdenum carbide-carbon nanocomposite carrier.

3. The catalyst for electrochemical hydrogen reaction under alkaline conditions according to claim 1, characterized in that, The ruthenium content in the catalyst is 1-15% by weight.

4. The catalyst for electrochemical hydrogen reaction under alkaline conditions according to claim 1, characterized in that, The molybdenum carbide-carbon nanocomposite carrier has a porous structure.

5. The catalyst for electrochemical hydrogen reaction according to claim 1, characterized in that, The electrochemical hydrogen reaction is either a hydrogen evolution reaction or a hydrogen oxidation reaction.

6. A catalytic electrode for use in anion exchange membrane water electrolysis or fuel cells, characterized in that, The catalyst comprising any one of claims 1 to 5.

7. A method for preparing a catalyst, comprising the steps described in claim 1: Step (A): Mix the ruthenium precursor and the molybdenum precursor with a solution containing a carbon precursor; Step (B) involves evaporating the solvent in the mixed solution to generate a thin film; Step (C): The film is subjected to a first heat treatment followed by micronization; as well as Step (D) involves subjecting the micronized catalyst to a second heat treatment.

8. The catalyst preparation method according to claim 7, characterized in that, The ruthenium precursor is ruthenium acetylacetonate.

9. The catalyst preparation method according to claim 7, characterized in that, The carbon precursor is polyethylene oxide-block polystyrene (PEO-b-PS), phenolic resin (PF resin), or melamine-formaldehyde resin (MF resin), and the molybdenum precursor is phosphomolybdic acid.

10. The catalyst preparation method according to claim 7, characterized in that, The first heat treatment is performed at 80–200°C. The second heat treatment includes the following steps: Step (D1): The micronized catalyst is fed into a tubular calcination furnace and heat-treated in an argon gas flow at 300-600°C for 1-10 hours and at 700-1,000°C for 2-15 hours. Then it is cooled to room temperature and passivated in a mixed gas flow of oxygen and argon for 5-30 hours before being micronized. Step (D2): The micropowder obtained in step (D1) is heat-treated in a mixed gas flow of oxygen and argon at 100–200°C for 2–15 hours, then cooled to room temperature and micronized; and Step (D3) involves heat-treating the micropowder obtained in step (D2) at 700–2,000°C for 2–15 hours in an argon gas flow, then cooling it to room temperature, and passivating it by holding it in a mixed gas flow of oxygen and argon for 5–30 hours before micronization.

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